mypy fails for a simple `Any` type alias`

[srittau]

I can't reproduce this locally, but please have a look at the CI failures of python/typeshed#7535. The change is a simple type alias Incomplete = Any. The TypeAlias is optional, mypy fails with or without it. CI runs mypy 0.941 with all Python versions.

[AlexWaygood]

#12134 (by @sobolevn) contains a fix for this bug. I think it might be good to excise that fix into a standalone PR.

[JukkaL]

I'll extract the Any fix from #12134 to a standalone PR. (cc @sobolevn)

[JukkaL]

Extracted the fix to #12429. The issue seems specific to typeshed (and possibly typeshed tests, in particular), and only reproduces for me if the files are passed to mypy in a specific order in the typeshed mypy test. I was able to reproduce it on macOS occasionally by randomizing the order of files passed to mypy.