ci: Move DCO check to the end of the pipeline
ci: Move DCO check to the end of the pipeline

This is consistent with what we do for other subprojects, and
allows changes that are not ready to be submitted to undergo
testing while still preventing accidental merge by failing the
pipeline.

Signed-off-by: Andrea Bolognani <3ada0bee826c753786fdbba72243dfba997094cf@redhat.com>

libvirt/ruby-libvirt,libvirt/ruby-libvirt,libvirt/ruby-libvirt