[flake8-pyi] Fix false negative for PYI046 with unused generic protocols (#9405)
I just fixed this false negative in flake8-pyi
(https://github.com/PyCQA/flake8-pyi/pull/460), and then realised ruff
has the exact same bug! Luckily it's a very easy fix.
(The bug is that unused protocols go undetected if they're generic.)