[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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nosy: +AlexWaygood, gvanrossum, kj

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue46611>
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