[#534] Websub fix: made SQL use UTC time zone when comparing with valid_until (instead of postgresql-server default time zone).

lib/pleroma/web/websub/websub.ex

@@ -64,7 +64,7 @@ def publish(topic, user, %{data: %{"type" => type}} = activity)
       from(
         sub in WebsubServerSubscription,
         where: sub.topic == ^topic and sub.state == "active",
-        where: fragment("? > NOW()", sub.valid_until)
+        where: fragment("? > (NOW() at time zone 'UTC')", sub.valid_until)
       )
 
     subscriptions = Repo.all(query)