🔧 Build: Skip RabbitMQ install in CI

Add `ci_skip` to the RabbitMQ task to prevent CI failures when running inside a Docker
container, where no systemd is available.

The CI previously managed to start `rabbitmq-server` in Docker despite the absence of
systemd. As of `rabbitmq-server 3.12.1-1ubuntu1.3`, the Ubuntu package explicitly blocks
`dh_installinit` in favour of `dh_systemd_start`, likely removing the SysV fallback that
Ansible's `service` module was relying on. The result is:

    Could not find the requested service rabbitmq-server: host

Since the AiiDA daemon (the primary RabbitMQ consumer) is already skipped in Docker via
`when: daemon_service is defined and daemon_service`, skipping RabbitMQ itself in the CI
is reasonable.

Author: mbercx

playbook-build.yml

@@ -132,7 +132,7 @@
   # TODO control version
   # could install with conda, but how to set up the systemd service?
   - name: Install RabbitMQ server service
-    tags: [rabbitmq]
+    tags: [rabbitmq, ci_skip]
     become: true
     become_user: "{{ root_user }}"
     ansible.builtin.import_tasks: local/tasks/rabbitmq.yml