Validate backup script before installation

roles/backups/tasks/main.yml

@@ -50,6 +50,10 @@
       - prosody:/data/docker/prosody:ro
       - synapse:/data/docker/synapse:ro
       - vaultwarden:/data/docker/vaultwarden:ro
+- name: Install shellcheck
+  become: true
+  ansible.builtin.apt:
+    name: shellcheck
 - name: Copy backup script
   become: true
   ansible.builtin.template:
@@ -57,6 +61,7 @@
     dest: /root/backup.sh
     mode: "0700"
     owner: root
+    validate: shellcheck %s
 - name: Configure backup job
   become: true
   ansible.builtin.cron: