generate warning if there's no plan in observer response (#1550)

skyvern/forge/sdk/services/observer_service.py

@@ -391,6 +391,10 @@ async def run_observer_cruise_helper(
             output={"task_type": task_type, "user_goal_achieved": user_goal_achieved},
         )
 
+        if not plan:
+            LOG.warning("No plan found in observer response", observer_response=observer_response)
+            continue
+
         if user_goal_achieved is True:
             LOG.info(
                 "User goal achieved. Workflow run will complete. Observer is stopping",