Update CI to reasonable versions and fix resulting issues

Our current CI config is too old to support collections. The version of ansible-lint we used is several major versions and significant changes behind.

For now, just use a plain Alpine Linux image and install the required software on the fly (it’s fast enough) and consider whether to build a custom image at another time.

alertmanager/handlers/main.yml

 ---
 
 - name: Restart alertmanager
-  systemd:
+  ansible.builtin.systemd:
     name: prometheus-alertmanager.service
     state: restarted
 
 - name: Reload alertmanager
-  systemd:
+  ansible.builtin.systemd:
     name: prometheus-alertmanager.service
     state: reloaded