fix: accept pseudo option in LocatorAssertions.not_to_have_css (#3244)

[Abhinav Maurya (Fire162)]

Fixes #3244.

LocatorAssertions.not_to_have_css rejected the pseudo parameter that to_have_css accepted, causing TypeError: LocatorAssertions.not_to_have_css() got an unexpected keyword argument 'pseudo'.

This PR:

1. Adds pseudo: Literal["after", "before"] = None to not_to_have_css in playwright/_impl/_assertions.py and forwards it to self._not.to_have_css.
2. Updates generated sync and async LocatorAssertions.not_to_have_css wrappers in playwright/async_api/_generated.py and playwright/sync_api/_generated.py.
3. Adds regression tests for to_have_css and not_to_have_css using pseudo="before" in both async and sync assertion test suites.

[Pavel Feldman (pavelfeldman)]

Thanks for the report and the fix! The public API is now generated from the upstream docs, so _generated.py can't be edited by hand: the next regeneration would drop the change. We added the option to the docs in microsoft/playwright#43414 and made the Python change in #3261. Closing this in favor of that one.