copr-be: rsnapshot-push: run weekly on Saturday

The process is I/O intensive, and we seem to have lower traffic on
weekends.

roles/rsnapshot-push/tasks/main.yml

@@ -66,10 +66,10 @@
 
 - name: cronjob run twice a week to trigger the backup (and rotation)
   cron:
-    name: "backup documents - {{ item.key }}"
+    name: "rsnapshot_push backup - {{ item.key }}"
     minute: "1"
     hour: "1"
-    day: "3,7"
+    weekday: "6"
     user: "{{ item.value.user }}"
     job: "ionice --class=idle /usr/local/bin/{{ item.value.command }} >/dev/null"
   with_dict: