gitlab: Convert check-dco/check-patch jobs to the 'rules' syntax

gitlab: Convert check-dco/check-patch jobs to the 'rules' syntax

Per GitLab documentation [*]:

  "rules replaces only/except and they can’t be used together
   in the same job."

Since the 'rules' syntax is more powerful and we are already using
it, convert the check-dco/check-patch jobs so no job use the 'only/
except' syntax.

[*] https://docs.gitlab.com/ee/ci/yaml/#rules

Inspired-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Message-Id: <20210525132418.4133235-3-f4bug@amsat.org>