[aiofiles] Fix NamedTemporaryFile name type

[nightcityblade]

Fixes #13551.

Narrows name to str only on wrappers returned by aiofiles.tempfile.NamedTemporaryFile(), while retaining the broader type on general async file wrappers.

OpenAI Codex was used to prepare this change.

[donbarbos]

Please remove the tests. In typeshed, we only add regression tests for functions and classes which are known to have caused complex problems in the past, or where stubs are difficult to get right. 100% test coverage for typeshed is neither necessary nor desirable, as it would lead to code duplication.

See tests/REGRESSION.md for more information.

[nightcityblade]

Removed the regression test in 72d696c as requested. I reran python tests/runtests.py stubs/aiofiles --run-stubtest; all aiofiles checks passed (pre-commit, structure, Pyright, ty, pyrefly, mypy, and stubtest).

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[JelleZijlstra]

This is incorrect, it returns a bytes name with NamedTemporaryFile(suffix=b""). Probably this should be generic over AnyStr?