Fix ParamType typing for Click 8.4

[adamtheturtle]

Fixes #200.

[janluke]

Hello! Thanks for the PR. Have you tested this with both Click 8.3 and 8.4? Have you run mypy as well with both?

[adamtheturtle]

Hi @janluke, thanks for the review!

Yes, tested with both Click 8.3.3 and Click 8.4.1 (Python 3.12, mypy 2.1.0). Results:

Click	pytest	mypy --strict cloup
8.3.3, master	328 pass	2 errors in cloup/_commands.py (pre-existing)
8.3.3, this PR	328 pass	same 2 errors, no regression
8.4.1, master	328 pass	3 errors: same 2, plus _params.pyi:14: Missing type arguments for generic type "ParamType"
8.4.1, this PR	328 pass	back to the same 2 pre-existing errors; the 8.4 typing error is fixed

So this PR cleanly resolves the new ParamType typing error on Click 8.4 without breaking 8.3.

The two remaining _commands.py errors are unrelated (isinstance(self, click.MultiCommand), since MultiCommand is deprecated in Click 8). I've opened #202 to track them and #203 with a one-line fix.