restic: Skip repo init on backup containers

Only the initial 'main' prune container will init the repository, the
others will not attempt even if they don't find a repository.

roles/grocy/templates/docker-compose.yaml.j2

@@ -22,6 +22,7 @@ services:
     hostname: "{{ ansible_hostname }}"
     environment:
       TZ: "{{ restic_tz }}"
+      SKIP_INIT: true
       BACKUP_CRON: "{{ stack_grocy_restic_cron }}"
       RESTIC_REPOSITORY: "{{ restic_repo }}"
       RESTIC_PASSWORD: "{{ restic_pass }}"