ci: Convert DCO job from 'except' to 'rules'
ci: Convert DCO job from 'except' to 'rules'

The former is the legacy syntax, while the latter is the current,
more flexible best practice.

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

libvirt/libvirt-glib,libvirt/libvirt-glib,libvirt/libvirt-glib