stubtest: Honor VERSIONS file for sub-modules

[srittau]

Bug Report

Cf. python/typeshed#6789. Currently, stubtest doesn't honor version ranges in stdlib's VERSIONS file. For example, when testing stdlib with Python 3.9, stubtest will complain about asyncio.mixins failed to find stubs, even though asyncio.mixins is marked as asyncio.mixins: 3.10- in VERSIONS.

Your Environment

• Mypy version used: as of today, typeshed uses mypy 0.931

[srittau]

Cc @sobolevn

[sobolevn]

Thanks, @srittau!

[sobolevn]

I am able to reproduce it locally, let's see why it happens.