ruff is a drop-in replacement for black, flake8 and isort, but runs
about 100 times faster.
Ref: https://github.com/astral-sh/ruff

On Studio, black accepts all the changes ruff makes.

This commit applies what ruff did, and removed a superfluous command in
test/run.py that ruff flagged, but does not change pre-commit or the dev
dependencies yet.

Also, revert this commit:
 2023-09-13 acd724e Eric Joanis ci: suppress redundant tests runs on PR and push
It turns out doing CI on review_requested is not great, because:
 - if you request 2 or 3 reviews, it triggers the action 2 or 3 times
 - when the branch needs a real merge, we do want the result of the merge
   tested in CI, so we lost important validation