Update backend-pull-notifications image to version 4

Linked build commit: 8606c8c587

backend-pull-notifications/deployment.yaml

@@ -50,7 +50,7 @@ spec:
               mountPath: /etc/secrets
       containers:
         - name: backend-pull-notifications
-          image: ghcr.io/gansejunge/app-notifications-backend-pull-notifications:3
+          image: ghcr.io/gansejunge/app-notifications-backend-pull-notifications:4
           ports:
             - containerPort: 8101
           env: