Fix include_subclasses strategy with a generic parent and tagged_union

[danarmak]

This extends the fix in #650 to the tagged union strategy. I reported the issue in #682.

Without this, using include_subclasses with tagged_union and a generic parent class raises the error AttributeError: __subclasses__. Did you mean: '__subclasscheck__'?.

Note: I don't know whether to edit default_tag_generator to say return (typing.get_origin(typ) or typ).__name__. It doesn't break any tests, but I'm not sure if there are cases where it wouldn't be appropriate, or what else ought to be changed if this is. For now I left it as a tag_generator override at the callsite, but it would be better for users not to have to pass this. Please advise.

The tests don't pass for me locally on the main branch (regardless of my change), but the failure is in a test that doesn't use these strategies and all the tests passed when I rebased my fix on 25.1.1, so I hope I'm just confused about something unrelated. (The failure is tests/test_gen_dict.py::test_individual_overrides - assert 'Factory' not in "{'a': ('', ... '_b': None}")

(ETA: the tests now pass, see comments)

[Tinche]

Thanks, I'll take a look when I get some free cycles. Can you get me a more detailed error message on that flaky test in the meantime?

[danarmak]

Here is the failing test output.

[Tinche]

Cool, thanks. Can you rebase, I reworked those tests.

[danarmak]

I rebased. All tests now pass.