Revert "Unblacklist /upgrade creates a new room (#7228)" (#7254)

This reverts commit 59f0ca8b.

.buildkite/worker-blacklist

@@ -5,6 +5,8 @@ Message history can be paginated
 
 Can re-join room if re-invited
 
+/upgrade creates a new room
+
 The only membership state included in an initial sync is for all the senders in the timeline
 
 Local device key changes get to remote servers

changelog.d/7228.misc

-Unblacklist '/upgrade creates a new room' sytest for workers.
\ No newline at end of file