v-m/alerts: Ignore missing backups from Toad, Luma

Toad and Luma can go offline for several days at a time if I don't use
them.  I don't need an alert telling me this.

victoria-metrics/alerts.yml

@@ -225,7 +225,10 @@ groups:
         the issue as soon as possible.
   - alert: Last Backup Age
     expr: >-
-      time() - restic_backup_timestamp > 604800
+      time() - restic_backup_timestamp{
+        client_hostname!="luma.pyrocufflink.blue",
+        client_hostname!="toad.pyrocufflink.blue",
+      }> 604800
     annotations:
       summary: A Restic client has not backed up recently
       description: >-