Don't fetch entire live revision

wagtail/actions/publish_revision.py

@@ -118,7 +118,7 @@ class PublishRevisionAction:
             # And clear the approved_go_live_at of any other revisions
             object.revisions.exclude(id=revision.id).update(approved_go_live_at=None)
             # if we are updating a currently live object skip the rest
-            if object.live_revision:
+            if object.live_revision_id:
                 # Log scheduled publishing
                 if log_action:
                     self.log_scheduling_action()