[ci] follow-up to !8 which neglected to set a default rule jobs

The changed merged in !8 (merged) prevented most jobs from running, because if you add a rules: section to the job, and none of the listed rules match, then the default is not run that job at all.

I'm still a little concerned that this isn't quite right: When I pushed the branch for this fix, it re-ran the setup jobs even though there is no .rebuild_cache file and the environment.yml files didn't exist. So by default it should never run the setup jobs unless one of those rules is satisfied.