TYP: simple return types from ruff

[twoertwein]

Ruff has many "unsafe" autofixes for simple return types.

I hope to enable --unsafe-fixes (for only the type annotations) after a few PRs.

[mroeschke]

Thanks @twoertwein

[jorisvandenbossche]

Is it needed to add -> None to test functions? (generally our test_.. test functions don't have any type annotations at all, I think?)

[twoertwein]

Is it needed to add -> None to test functions? (generally our test_.. test functions don't have any type annotations at all, I think?)

I think it would be good to exclude pandas/tests (and scripts/tests - happy to revert that) from these ruff fixes! I don't think it would add value for the tests (unless people prefer it for consistency).

However, manually adding annotations for tests can be valuable to selectively allow mypy to run on some tests to help with #45252. I believe most test files are completely ignored and unannotated functions are anyways skipped: so we could use -> None to run mypy on a subset of tests within a file.