Update attachment string.

strato-production.yaml

@@ -67,7 +67,7 @@
             subject: Datenbank Backup
             body: System {{ ansible_hostname }} has been successfully provisioned.
             attach:
-            - {{ backup_dir }}/{{ item }}/db-{{ ansible_date_time.iso8601_basic_short }}.sql.gz
+            - "{{ backup_dir }}/{{ item }}/db-{{ ansible_date_time.iso8601_basic_short }}.sql.gz"
           delegate_to: localhost
           when: item.value.email is defined
           loop: "{{ lookup('dict', customers) }}"