[issue46345] Add an explicit test for `get_type_hints` for a class field with `None` default

[Nikita Sobolev]

Change by Nikita Sobolev <mail at sobolevn.me>:


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keywords: +patch
pull_requests: +28736
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/30535

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<https://bugs.python.org/issue46345>
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