Reference Issues/PRs

Towards #27676

What does this implement/fix? Explain your changes.

CallbackSupportMixin.set_callbacks verify that the provided callbacks are valid by using isinstance with the callback protocol. But isinstance with protocols also accepts classes, so passing the class of a valid callback would pass the test in set_callbacks and create problems later.

The change simply adds a inspect.isclass test to reject classes and only accept instances.

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• Code generation (e.g., when writing an implementation or fixing a bug)
• Test/benchmark generation
• Documentation (including examples)
• Research and understanding

Any other comments?

ping @jeremiedbb @ogrisel @StefanieSenger @lesteve