All system checks do not run with manage.py gunicorn

Some system checks we use have a @only_runserver decorator to restrict them to when manage.py runserver is used, since some are irrelevant for unit tests or other simpler tasks. This decorator uses settings.ALL_CHECKS, which is set to True only if the ALL_CHECKS environment variable is set to true, or when runserver is in sys.argv.

I added a dumb system check to verify this:

@register()
@only_runserver
def lol(*args, **kwargs):
    return [
        Critical('You have summoned Cthulhu', id='arkindex.C666')
    ]

Running manage.py runserver or running any command with ALL_CHECKS=true manage.py … does show that I have delved too deep in dark arts, but running manage.py gunicorn or arkindex gunicorn either inside or outside of Docker did not show any error.

Since ALL_CHECKS is not set in teklia/infra, this means that some system checks are currently not running at all in production.