Branches no longer need a pull request to master to be tested; a
branch is checked when it is pushed and lands on master by
fast-forward once it is green. Pull requests to master still run the
checks. CodeQL keeps running on master, its pull requests and its
weekly schedule.
Super-linter ran from the unpinned :latest image and, because of
branches-ignore: [master], never on pull requests to master. Ruff now
checks syntax errors and pyflakes rules (E9, F) on every push and PR.
Fixes the existing findings: unused imports and variables, an unused
duplicate import in instances/tests.py, and the star import in
accounts/views.py. settings-dev.py keeps its star import of the base
settings.
