The "clone" strategy clones the entire repository, which takes
a significant amount of time. It's not needed, because the default
"fetch" strategy will reuse the executor's local clone and clean it
before the job scripts run.

There's no need to let these artifacts pile up since the only ones that
will be relevant to non-programmers are the latest from any given ref.

The singular .gitlab-ci.yml is pretty beefy. Splitting it into
smaller files by job and job template will make maintaining the
individual jobs easier.