fix: set `pipefail` flag in shell commands using pipes

Without `pipefail` Ansible cannot detect if there is an error executing
the command before the pipe as the return code of the shell only
reflects the return code of the last command. As not all shells support
`pipefail` (e.g., `ash`, `dash`) we also enfore the use of `bash` in
this case.

ansible/maintenance/maint-diskspace.yaml

@@ -4,7 +4,11 @@
 
   tasks:
     - name: Check disk space available
-      ansible.builtin.shell: df -Ph / | awk 'NR==2 {print $5}'
+      ansible.builtin.shell:
+        cmd: |
+          set -euo pipefail
+          df -Ph / | awk 'NR==2 {print $5}'
+        executable: /bin/bash
       register: disk_usage
 
     # - name: Send discord message when disk space is over 80%