Test filtering in tox.ini is imprecise

[bkeryan]

Tech Debt

-k "not grpc" filters out tests that contain grpc in their name or use the grpc_init_kwargs fixture, but unfortunately it also seems to filter out tests that have a grpc_skip marker.

-k "library" only runs tests that contain library in their name or use the library_init_kwargs fixture, and unfortunately it also filters out tests that are not specific to library or grpc, such as feature toggle tests.

AB#3354823