fix return

openhands/controller/agent.py

@@ -50,7 +50,7 @@ def complete(self) -> bool:
         return self._complete
 
     @abstractmethod
-    def step(self, state: 'State') -> Action:
+    def step(self, state: 'State') -> 'Action':
         """Starts the execution of the assigned instruction. This method should
         be implemented by subclasses to define the specific execution logic.
         """