[JIT] Fix typing.Final for python 3.8 (#39568)
Summary:
fixes https://github.com/pytorch/pytorch/issues/39566
`typing.Final` is a thing since python 3.8, and on python 3.8, `typing_extensions.Final` is an alias of `typing.Final`, therefore, `ann.__module__ == 'typing_extensions'` will become False when using 3.8 and `typing_extensions` is installed.
~~I don't know why the test is skipped, seems like due to historical reason when python 2.7 was still a thing?~~ Edit: I know now, the `Final` for `<3.7` don't have `__origin__`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39568
Reviewed By: smessmer
Differential Revision: D23043388
Pulled By: malfet
fbshipit-source-id: cc87a9e4e38090d784e9cea630e1c543897a1697
