Add test case for Alma9
Now that CentOS7 is slowly being phased out, it would be nice to have a test running on Alma9.
Unfortunately the CERN CI tools registry has no Alma9 image: https://gitlab.cern.ch/ci-tools/ci-worker
And the base Alma9 image gitlab-registry.cern.ch/linuxsupport/alma9-base
is missing too many dependencies to be usable...