fix find command to delete old backup

templates/brain_backup.j2

@@ -238,7 +238,7 @@ mkdir -p "$backup_dir/$today/sshportal"
 {% endif %}
 
 # purge old backups
-find $backup_dir -type d -ctime +$backup_local_retention -exec rm -rf {} \;
+find $backup_dir -maxdepth 1 -mindepth 1 -type d -mtime +$backup_local_retention -exec rm -rf {} \;
 
 ## send to PBS ##
 /usr/bin/proxmox-backup-client backup \