Downgrade PyYAML to fix build issue (#41)

See the following GitHub issues for more info:

- yaml/pyyaml#724
- yaml/pyyaml#601
- yaml/pyyaml#723

```
 => ERROR [stage-1 4/4] RUN pip install --no-deps -r /tmp/requirements.txt &&   pip install /tmp/marge-*.tar.gz                                                                                                                                                                                      4.8s
------
 > [stage-1 4/4] RUN pip install --no-deps -r /tmp/requirements.txt &&   pip install /tmp/marge-*.tar.gz:
0.995 Ignoring backports-zoneinfo: markers 'python_version >= "3.7" and python_version < "3.9"' don't match your environment
0.995 Ignoring importlib-metadata: markers 'python_version >= "3.7" and python_version < "3.8"' don't match your environment
0.996 Ignoring typing-extensions: markers 'python_version >= "3.7" and python_version < "3.8"' don't match your environment
0.996 Ignoring zipp: markers 'python_version >= "3.7" and python_version < "3.8"' don't match your environment
1.049 Collecting certifi==2022.12.7
1.084   Downloading certifi-2022.12.7-py3-none-any.whl (155 kB)
1.107      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 155.3/155.3 kB 6.7 MB/s eta 0:00:00
1.178 Collecting charset-normalizer==3.1.0
1.189   Downloading charset_normalizer-3.1.0-cp310-cp310-manylinux_2_17_x86_64.manylinux2014_x86_64.whl (199 kB)
1.197      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 199.3/199.3 kB 26.0 MB/s eta 0:00:00
1.214 Collecting configargparse==1.5.3
1.225   Downloading ConfigArgParse-1.5.3-py3-none-any.whl (20 kB)
1.245 Collecting dateparser==1.1.8
1.260   Downloading dateparser-1.1.8-py2.py3-none-any.whl (293 kB)
1.271      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 293.8/293.8 kB 28.9 MB/s eta 0:00:00
1.290 Collecting decorator==5.1.1
1.300   Downloading decorator-5.1.1-py3-none-any.whl (9.1 kB)
1.324 Collecting humanize==4.6.0
1.337   Downloading humanize-4.6.0-py3-none-any.whl (109 kB)
1.341      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 110.0/110.0 kB 31.5 MB/s eta 0:00:00
1.363 Collecting idna==3.4
1.374   Downloading idna-3.4-py3-none-any.whl (61 kB)
1.377      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 61.5/61.5 kB 26.5 MB/s eta 0:00:00
1.493 Collecting maya==0.6.1
1.515   Downloading maya-0.6.1-py2.py3-none-any.whl (12 kB)
1.562 Collecting pendulum==2.1.2
1.573   Downloading pendulum-2.1.2.tar.gz (81 kB)
1.577      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 81.2/81.2 kB 27.5 MB/s eta 0:00:00
1.596   Installing build dependencies: started
2.239   Installing build dependencies: finished with status 'done'
2.240   Getting requirements to build wheel: started
2.287   Getting requirements to build wheel: finished with status 'done'
2.287   Preparing metadata (pyproject.toml): started
2.420   Preparing metadata (pyproject.toml): finished with status 'done'
2.445 Collecting python-dateutil==2.8.2
2.456   Downloading python_dateutil-2.8.2-py2.py3-none-any.whl (247 kB)
2.466      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 247.7/247.7 kB 27.7 MB/s eta 0:00:00
2.480 Collecting pytz-deprecation-shim==0.1.0.post0
2.491   Downloading pytz_deprecation_shim-0.1.0.post0-py2.py3-none-any.whl (15 kB)
2.534 Collecting pytz==2023.3
2.546   Downloading pytz-2023.3-py2.py3-none-any.whl (502 kB)
2.564      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 502.3/502.3 kB 29.6 MB/s eta 0:00:00
2.585 Collecting pytzdata==2020.1
2.598   Downloading pytzdata-2020.1-py2.py3-none-any.whl (489 kB)
2.620      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 490.0/490.0 kB 23.4 MB/s eta 0:00:00
2.663 Collecting pyyaml==5.4.1
2.675   Downloading PyYAML-5.4.1.tar.gz (175 kB)
2.682      ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 175.1/175.1 kB 29.7 MB/s eta 0:00:00
2.778   Installing build dependencies: started
4.419   Installing build dependencies: finished with status 'done'
4.420   Getting requirements to build wheel: started
4.562   Getting requirements to build wheel: finished with status 'error'
4.568   error: subprocess-exited-with-error
4.568
4.568   × Getting requirements to build wheel did not run successfully.
4.568   │ exit code: 1
4.568   ╰─> [62 lines of output]
4.568       /tmp/pip-build-env-xmsfsb8h/overlay/lib/python3.10/site-packages/setuptools/config/setupcfg.py:293: _DeprecatedConfig: Deprecated config in `setup.cfg`
4.568       !!
4.568
4.568               ********************************************************************************
4.568               The license_file parameter is deprecated, use license_files instead.
4.568
4.568               By 2023-Oct-30, you need to update your project and remove deprecated calls
4.568               or your builds will no longer be supported.
4.568
4.568               See https://setuptools.pypa.io/en/latest/userguide/declarative_config.html for details.
4.568               ********************************************************************************
4.568
4.568       !!
4.568         parsed = self.parsers.get(option_name, lambda x: x)(value)
4.568       running egg_info
4.568       writing lib3/PyYAML.egg-info/PKG-INFO
4.568       writing dependency_links to lib3/PyYAML.egg-info/dependency_links.txt
4.568       writing top-level names to lib3/PyYAML.egg-info/top_level.txt
4.568       Traceback (most recent call last):
4.568         File "/usr/local/lib/python3.10/site-packages/pip/_vendor/pep517/in_process/_in_process.py", line 351, in <module>
4.568           main()
4.568         File "/usr/local/lib/python3.10/site-packages/pip/_vendor/pep517/in_process/_in_process.py", line 333, in main
4.568           json_out['return_val'] = hook(**hook_input['kwargs'])
4.568         File "/usr/local/lib/python3.10/site-packages/pip/_vendor/pep517/in_process/_in_process.py", line 118, in get_requires_for_build_wheel
4.568           return hook(config_settings)
4.568         File "/tmp/pip-build-env-xmsfsb8h/overlay/lib/python3.10/site-packages/setuptools/build_meta.py", line 355, in get_requires_for_build_wheel
4.568           return self._get_build_requires(config_settings, requirements=['wheel'])
4.568         File "/tmp/pip-build-env-xmsfsb8h/overlay/lib/python3.10/site-packages/setuptools/build_meta.py", line 325, in _get_build_requires
4.568           self.run_setup()
4.568         File "/tmp/pip-build-env-xmsfsb8h/overlay/lib/python3.10/site-packages/setuptools/build_meta.py", line 341, in run_setup
4.568           exec(code, locals())
4.568         File "<string>", line 271, in <module>
4.568         File "/tmp/pip-build-env-xmsfsb8h/overlay/lib/python3.10/site-packages/setuptools/__init__.py", line 103, in setup
4.568           return distutils.core.setup(**attrs)
4.568         File "/tmp/pip-build-env-xmsfsb8h/overlay/lib/python3.10/site-packages/setuptools/_distutils/core.py", line 185, in setup
4.568           return run_commands(dist)
4.568         File "/tmp/pip-build-env-xmsfsb8h/overlay/lib/python3.10/site-packages/setuptools/_distutils/core.py", line 201, in run_commands
4.568           dist.run_commands()
4.568         File "/tmp/pip-build-env-xmsfsb8h/overlay/lib/python3.10/site-packages/setuptools/_distutils/dist.py", line 969, in run_commands
4.568           self.run_command(cmd)
4.568         File "/tmp/pip-build-env-xmsfsb8h/overlay/lib/python3.10/site-packages/setuptools/dist.py", line 989, in run_command
4.568           super().run_command(command)
4.568         File "/tmp/pip-build-env-xmsfsb8h/overlay/lib/python3.10/site-packages/setuptools/_distutils/dist.py", line 988, in run_command
4.568           cmd_obj.run()
4.568         File "/tmp/pip-build-env-xmsfsb8h/overlay/lib/python3.10/site-packages/setuptools/command/egg_info.py", line 318, in run
4.568           self.find_sources()
4.568         File "/tmp/pip-build-env-xmsfsb8h/overlay/lib/python3.10/site-packages/setuptools/command/egg_info.py", line 326, in find_sources
4.568           mm.run()
4.568         File "/tmp/pip-build-env-xmsfsb8h/overlay/lib/python3.10/site-packages/setuptools/command/egg_info.py", line 548, in run
4.568           self.add_defaults()
4.568         File "/tmp/pip-build-env-xmsfsb8h/overlay/lib/python3.10/site-packages/setuptools/command/egg_info.py", line 586, in add_defaults
4.568           sdist.add_defaults(self)
4.568         File "/tmp/pip-build-env-xmsfsb8h/overlay/lib/python3.10/site-packages/setuptools/command/sdist.py", line 113, in add_defaults
4.568           super().add_defaults()
4.568         File "/tmp/pip-build-env-xmsfsb8h/overlay/lib/python3.10/site-packages/setuptools/_distutils/command/sdist.py", line 251, in add_defaults
4.568           self._add_defaults_ext()
4.568         File "/tmp/pip-build-env-xmsfsb8h/overlay/lib/python3.10/site-packages/setuptools/_distutils/command/sdist.py", line 336, in _add_defaults_ext
4.568           self.filelist.extend(build_ext.get_source_files())
4.568         File "<string>", line 201, in get_source_files
4.568         File "/tmp/pip-build-env-xmsfsb8h/overlay/lib/python3.10/site-packages/setuptools/_distutils/cmd.py", line 107, in __getattr__
4.568           raise AttributeError(attr)
4.568       AttributeError: cython_sources
4.568       [end of output]
4.568
4.568   note: This error originates from a subprocess, and is likely not a problem with pip.
4.569 error: subprocess-exited-with-error
4.569
4.569 × Getting requirements to build wheel did not run successfully.
4.569 │ exit code: 1
4.569 ╰─> See above for output.
4.569
4.569 note: This error originates from a subprocess, and is likely not a problem with pip.
4.571
4.571 [notice] A new release of pip available: 22.3.1 -> 23.2.1
4.571 [notice] To update, run: pip install --upgrade pip
```