gitlab-ci: Do not download artifacts of unrelated builds

gitlab-ci: Do not download artifacts of unrelated builds

This needs: is overridden in many cases, but ensures none of the other
main jobs start until this build finishes.  However this also
ensures we do not download artifacts from any build unless we
specifically depend on it, saving bandwidth

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14863

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>