[issue46611] Improve coverage of `__instancecheck__` and `__subclasscheck__` methods in `typing.py`

[Nikita Sobolev]

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


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keywords: +patch
pull_requests: +29262
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/31078

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<https://bugs.python.org/issue46611>
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