Re-run update status notification after the update

It may happen that no updates are available anymore (for example already
installed). In this case apt nor dnf run our notification hooks, so
informations about "no updates" is never send and template stays in
"updates available" state forever.

Fixes QubesOS/qubes-issues#4650

(cherry picked from commit 4ae92f8)

update/qubes-vm.sls

@@ -48,3 +48,6 @@ update:
       - cmd: dsa-4371-update
 {% endif %}
 
+notify-updates:
+  cmd.run:
+    - name: /usr/lib/qubes/upgrades-status-notify