notifications: dont return error if one notifer failed

pkg/services/alerting/notifier.go

@@ -90,7 +90,7 @@ func (n *notificationService) sendNotifications(evalContext *EvalContext, notifi
 		})
 
 		if err != nil {
-			return err
+			n.log.Error("failed to send notification", "id", not.GetNotifierId())
 		}
 	}