[3.15] Add `__class_getitem__` of classes

[JaeHyuckSa]

I have made things!

I added __class_getitem__ of classes in DRF version 3.15.

The following are class items with __class_getitem__ added.

• fields.Field.__class_getitem__
• generics.GenericAPIView.__class_getitem__
• request.Request.__class_getitem__
• response.Response.__class_getitem__

Related issues

Upstream PR: https://github.com/encode/django-rest-framework/pull/8825

[JaeHyuckSa]

All places, please :) Here are examples: https://github.com/search?q=repo%3Apython%2Ftypeshed%20__class_getitem__&type=code

Oh... I sincerely appreciate you providing an example!! I will repost the PR once the necessary modifications are completed.