gitea: use random time for git gc run

Randomising the time of this job should help avoid a thundering herd
of I/O intensive operations in the gitea environment.

Change-Id: I035f7781a397665357b6d039b989ab9fe6a46b8a

playbooks/roles/gitea/tasks/main.yaml

@@ -132,8 +132,8 @@
     name: pack-git-refs
     state: present
     job: "docker exec -t giteadocker_gitea-web_1 find /data/git/repositories/ -maxdepth 2 -name *.git -type d -execdir git --git-dir={} gc --quiet \\;"
-    minute: 37
-    hour: 12
+    minute: '{{ 59 | random(seed=inventory_hostname) }}'
+    hour: '{{ 23 | random(seed=inventory_hostname) }}'
     weekday: 0
 - name: Create db backup dest
   file: