Exclude sqlalchemy-spanner 1.12.0

[vincbeck]

I stumbled into that error while working and I can see some PRs having tests fail because of that. Example: #51375.

× Failed to build `sqlalchemy-spanner==1.12.0`
    ├─▶ The build backend returned an error
    ╰─▶ Call to `setuptools.build_meta:__legacy__.build_wheel` failed (exit
        status: 1)
  
        [stderr]
        Traceback (most recent call last):
          File "<string>", line 14, in <module>
          File
        "/home/runner/.cache/uv/builds-v0/.tmpYW7k7q/lib/python3.9/site-packages/setuptools/build_meta.py",
        line 331, in get_requires_for_build_wheel
            return self._get_build_requires(config_settings, requirements=[])
          File
        "/home/runner/.cache/uv/builds-v0/.tmpYW7k7q/lib/python3.9/site-packages/setuptools/build_meta.py",
        line 301, in _get_build_requires
            self.run_setup()
          File
        "/home/runner/.cache/uv/builds-v0/.tmpYW7k7q/lib/python3.9/site-packages/setuptools/build_meta.py",
        line 512, in run_setup
            super().run_setup(setup_script=setup_script)
          File
        "/home/runner/.cache/uv/builds-v0/.tmpYW7k7q/lib/python3.9/site-packages/setuptools/build_meta.py",
        line 317, in run_setup
            exec(code, locals())
          File "<string>", line 42, in <module>
        FileNotFoundError: [Errno 2] No such file or directory:
        '/home/runner/.cache/uv/sdists-v9/pypi/sqlalchemy-spanner/1.12.0/mxsH0MW5JmWIuTAq38DAJ/src/version.py'
  
        hint: This usually indicates a problem with the package or the build
        environment.
    help: `sqlalchemy-spanner` (v1.12.0) was included
          because `apache-airflow[all]` (v3.1.0) depends on
          `apache-airflow-providers-google` (v15.1.0) which depends on
          `sqlalchemy-spanner>=1.6.2`

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