[Notifications] Fix notifications pusher failing to initialize (#3654)

fix

Co-authored-by: quaark <a.melnick@icloud.com>

mlrun/utils/notifications/notification_pusher.py

@@ -51,7 +51,7 @@ def __init__(self, runs: typing.Union[mlrun.lists.RunList, list]):
             for notification in run.spec.notifications:
                 notification.status = run.status.notifications.get(
                     notification.name
-                ).status
+                ).get("status", mlrun.common.schemas.NotificationStatus.PENDING)
                 if self._should_notify(run, notification):
                     self._notification_data.append((run, notification))