Fix yields and copy instead of move push rules on room upgrade (#6144)

Copy push rules during a room upgrade from the old room to the new room, instead of deleting them from the old room.

For instance, we've defined upgrading of a room multiple times to be possible, and push rules won't be transferred on the second upgrade if they're deleted during the first.

Also fix some missing yields that probably broke things quite a bit.

synapse/handlers/room_member.py

@@ -216,8 +216,8 @@ class RoomMemberHandler(object):
                 self.copy_room_tags_and_direct_to_room(
                     predecessor["room_id"], room_id, user_id
                 )
-                # Move over old push rules
-                self.store.move_push_rules_from_room_to_room_for_user(
+                # Copy over push rules
+                yield self.store.copy_push_rules_from_room_to_room_for_user(
                     predecessor["room_id"], room_id, user_id
                 )
         elif event.membership == Membership.LEAVE: