Fix some typing issues

[euresti]

Pull Request Check List

This is just a reminder about the most common mistakes. Please make sure that you tick all appropriate boxes. But please read our contribution guide at least once, it will save you unnecessary review cycles!

If an item doesn't apply to your pull request, check it anyway to make it apparent that there's nothing to do.

• Added tests for changed code.
• New features have been added to our Hypothesis testing strategy.
• Changes or additions to public APIs are reflected in our type stubs (files ending in .pyi).
  • ...and used in the stub test file tests/typing_example.py.
• Updated documentation for changed code.
  • New functions/classes have to be added to docs/api.rst by hand.
  • Changes to the signature of @attr.s() have to be added by hand too.
  • Changed/added classes/methods/functions have appropriate versionadded, versionchanged, or deprecated directives.
• Documentation in .rst files is written using semantic newlines.
• Changes (and possible deprecations) have news fragments in changelog.d.

If you have any questions to any of the points above, just submit and ask! This checklist is here to help you, not to deter you from contributing!

[euresti]

Do you want a changelog for this?

[hynek]

Do you want a changelog for this?

I don’t think it has any user-visible effects, does it? I think it’s fine.

[hynek]

I cannot realistically review this but I don't want to block on it. If Ethan or someone else more familiar with typing, please pipe up. For now I'm merging it since mypy is telling me that it's an improvement. ¯\_(ツ)_/¯