[issue38978] Implement __class_getitem__ for Future, Task, Queue

[Batuhan]

Change by Batuhan <batuhanosmantaskaya at gmail.com>:


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keywords: +patch
pull_requests: +16969
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/17491

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue38978>
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