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

[miss-islington]

Change by miss-islington <mariatta.wijaya+miss-islington at gmail.com>:


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pull_requests: +28771
pull_request: https://github.com/python/cpython/pull/30568

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