Add changelog entry

Author: IvanIsCoding

newsfragments/4926.added.md

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+Introduced a new optional parameter with `#[pyclass(generic)]`. This new
+parameter makes classes support generic typing at the runtime following
+[PEP 560](https://peps.python.org/pep-0560/). It is an alternative
+to inheriting from [typing.Generic](https://docs.python.org/3/library/typing.html#typing.Generic).