taskotron/resultsdb-backend: Fix the mode to be string instead of integer

For unclear reason ansible seems to have issues with mode expressed
in integer while it seems to work much more nicely if they are
provided as string.
So moving to this for now.

Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>

roles/taskotron/resultsdb-backend/tasks/main.yml

@@ -74,17 +74,17 @@
       dest: resultsdb.crt
       owner: root
       group: apache
-      mode: 0644
+      mode: "444"
     - src: "{{private}}/files/rabbitmq/{{env}}/pki/private/resultsdb{{ env_suffix }}.key"
       dest: resultsdb.key
       owner: root
       group: apache
-      mode: 0640
+      mode: "440"
     - src: "{{private}}/files/rabbitmq/{{env}}/pki/ca.crt"
       dest: resultsdb.ca
       owner: root
       group: apache
-      mode: 0644
+      mode: "444"
   when: env == "staging"
   tags:
     - fedora-messaging