fix: ci: Use resource-group for RPM-related CI jobs

RPM build jobs work by pushing a commits to main in a repository. Each
repository is identified by the `SERVICE variable and, since race
conditions may happen, the jobs are run serially via GitLab's
resource_group mechanism.

Merge branch 'andoni/use-resource-group-for-rpms-copr-ci-job' into 'main'

See merge request isc-projects/bind9!12295