server/prune_job: add proper permission checks to 'prune_datastore'

checks for PRIV_DATASTORE_MODIFY, or else if the auth_id is the backup
owner, and skips the group if not.

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>

src/backup/datastore.rs

@@ -355,7 +355,7 @@ impl DataStore {
     pub fn owns_backup(&self, backup_group: &BackupGroup, auth_id: &Authid) -> Result<bool, Error> {
         let owner = self.get_owner(backup_group)?;
 
-        Ok(check_backup_owner(owner, auth_id).is_ok())
+        Ok(check_backup_owner(&owner, auth_id).is_ok())
     }
 
     /// Set the backup owner.