Fix worker documentation around room Admin APIs (#18853)

Discovered via https://github.com/element-hq/ess-helm/issues/677.
Looking at
https://github.com/element-hq/synapse/blob/v1.136.0/synapse/rest/admin/__init__.py#L266
only `RoomRestServlet` is generally worker capable. This is just the
Room Details API and the v1 Room Delete API and not all the APIs
documented on
https://element-hq.github.io/synapse/latest/admin_api/rooms.html

docs/workers.md

@@ -252,7 +252,7 @@ information.
     ^/_matrix/client/(api/v1|r0|v3|unstable)/directory/room/.*$
     ^/_matrix/client/(r0|v3|unstable)/capabilities$
     ^/_matrix/client/(r0|v3|unstable)/notifications$
-    ^/_synapse/admin/v1/rooms/
+    ^/_synapse/admin/v1/rooms/[^/]+$
 
     # Encryption requests
     ^/_matrix/client/(r0|v3|unstable)/keys/query$