CI is failing

[JelleZijlstra]

See #15989, #15986, #15965, #15987.

The failure looks like this:

  File "/opt/hostedtoolcache/Python/3.8.17/x64/lib/python3.8/site-packages/tox/tox_env/package.py", line 47, in _func
    return meth(*args, **kwargs)
  File "/opt/hostedtoolcache/Python/3.8.17/x64/lib/python3.8/site-packages/tox/tox_env/python/virtual_env/package/pyproject.py", line 292, in get_package_dependencies
    self._ensure_meta_present(for_env)
  File "/opt/hostedtoolcache/Python/3.8.17/x64/lib/python3.8/site-packages/tox/tox_env/package.py", line 47, in _func
    return meth(*args, **kwargs)
  File "/opt/hostedtoolcache/Python/3.8.17/x64/lib/python3.8/site-packages/tox/tox_env/python/virtual_env/package/pyproject.py", line 312, in _ensure_meta_present
    dist_info = end.prepare_metadata_for_build_wheel(self.meta_folder, self._wheel_config_settings).metadata
AttributeError: 'NoneType' object has no attribute 'metadata'

Which makes me think a release of tox or some other packaging tool is to blame. And indeed tox 4.11.0 was released earlier today (https://tox.wiki/en/latest/changelog.html#v4-11-0-2023-08-29).

[hauntsaninja]

We pin tox, probably because it's not uncommon for it to break CI. Looks to me maybe triggered by release for https://pypi.org/project/pyproject-api/ ?