Tests currently failing on setuptools>72

[kyluca]

While working on #254, I got an unrelated build failure and noticed the same occuring on main: https://github.com/tldr-pages/tldr-python-client/actions/runs/10634495107/job/29481939309

Run python3 setup.py pytest
/opt/hostedtoolcache/Python/3.9.19/x64/lib/python3.9/site-packages/setuptools/_distutils/dist.py:260: UserWarning: Unknown distribution option: 'tests_require'
  warnings.warn(msg)
/opt/hostedtoolcache/Python/3.9.19/x64/lib/python3.9/site-packages/ptr/__init__.py:81: SetuptoolsDeprecationWarning: The test command is disabled and references to it are deprecated.
!!

        ********************************************************************************
        Please remove any references to `setuptools.command.test` in all supported versions of the affected package.

        By 2024-Nov-15, you need to update your project and remove deprecated calls
        or your builds will no longer be supported.
        ********************************************************************************

!!
  class PyTest(orig.test):
running pytest
Traceback (most recent call last):
  File "/home/runner/work/tldr-python-client/tldr-python-client/setup.py", line 17, in <module>
    setup(
  File "/opt/hostedtoolcache/Python/3.9.19/x64/lib/python3.9/site-packages/setuptools/__init__.py", line 117, in setup
    return distutils.core.setup(**attrs)
  File "/opt/hostedtoolcache/Python/3.9.19/x64/lib/python3.9/site-packages/setuptools/_distutils/core.py", line 184, in setup
    return run_commands(dist)
  File "/opt/hostedtoolcache/Python/3.9.19/x64/lib/python3.9/site-packages/setuptools/_distutils/core.py", line 200, in run_commands
    dist.run_commands()
  File "/opt/hostedtoolcache/Python/3.9.19/x64/lib/python3.9/site-packages/setuptools/_distutils/dist.py", line 953, in run_commands
    self.run_command(cmd)
  File "/opt/hostedtoolcache/Python/3.9.19/x64/lib/python3.9/site-packages/setuptools/dist.py", line 950, in run_command
    super().run_command(command)
  File "/opt/hostedtoolcache/Python/3.9.19/x64/lib/python3.9/site-packages/setuptools/_distutils/dist.py", line 972, in run_command
    cmd_obj.run()
  File "/opt/hostedtoolcache/Python/3.9.19/x64/lib/python3.9/site-packages/ptr/__init__.py", line 195, in run
    setattr(dist, attr, getattr(self.distribution, attr))
AttributeError: 'Distribution' object has no attribute 'tests_require'
Error: Process completed with exit code 1.

I believe this is due to the line python3 setup.py pytest being used in the test.yml workflow.

Instead what we probably want is to invoke pytest directly, as per their docs.