fix(ci): check imports with the same isort as pre-commit

CI installs isort 5.13.2 from requirements.txt, while pre-commit runs
6.0.1. With the black profile, 6.x keeps an import exploded when it ends
in a trailing comma and 5.13 joins it back onto one line, so files the
hook had formatted failed CI's check (9 of them on this branch). Pin
6.0.1 in requirements.txt so the hook and CI agree.

kubernetes/client.py also had `from requests import Response` inside
the first-party block; it moves up to the third-party imports, where
both versions put it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>