When the whitespace job was added, we marked it with
because we wanted it to only run on new merge requests.
However, adding an
only clause like this disables all the
unmarked jobs for merge requests, which means we don't get
the more important feedback about build failures.
Instead, use the
rules key, added in Gitlab 12.3. This
more flexible mechanism is currently recommended and lets
us specify what we want without having to add additional
decorations to every other job.