Fix mypy failure after multiple merges

[Avasam]

Summary of changes

@abravalheri for https://github.com/pypa/setuptools/pull/4709#issuecomment-2450555145

As I thought, one PR made Distribution.get_command_class no longer return Any for mypy, the other made install.do_egg_install type-checked. Individually they both passed the CI.

Pull Request Checklist

• [ ] Changes have tests
• [ ] News fragment added in newsfragments/. (See [documentation][PR docs] for details)

[PR docs]: https://setuptools.pypa.io/en/latest/development/developer-guide.html#making-a-pull-request

[abravalheri]

Uh, though one. Thank you very much @Avasam.