Fix final forum phase select faction leader WS

Fix an issue where WebSocket messages for select faction leader actions were not being sent to clients during the final forum phase.

backend/rorapp/functions/faction_leader_helper.py

@@ -187,7 +187,7 @@ def proceed_to_next_step_if_forum_phase(game_id, step, faction) -> List[dict]:
 
         if next_faction is not None:
             if step.phase.name.startswith("Final"):
-                messages_to_send.extend(
+                messages_to_send.append(
                     generate_select_faction_leader_action(next_faction)
                 )
             else: