fix: fix event migrating handler in RequestQueue (#825)

### Description

- fix event migrating handler and `is_finished` method in `RequestQueue`

### Issues

- Closes: #815

Author: Mantisus

src/crawlee/storages/_request_queue.py

@@ -119,8 +119,8 @@ def __init__(self, id: str, name: str | None, storage_client: BaseStorageClient)
         self._queue_paused_for_migration = False
 
         event_manager.on(event=Event.MIGRATING, listener=lambda _: setattr(self, '_queue_paused_for_migration', True))
-        event_manager.on(event=Event.MIGRATING, listener=lambda _: self._clear_possible_locks())
-        event_manager.on(event=Event.ABORTING, listener=lambda _: self._clear_possible_locks())
+        event_manager.on(event=Event.MIGRATING, listener=self._clear_possible_locks)
+        event_manager.on(event=Event.ABORTING, listener=self._clear_possible_locks)
 
         # Other internal attributes
         self._tasks = list[asyncio.Task]()
@@ -494,7 +494,7 @@ async def is_finished(self) -> bool:
                 'Queue head still returned requests that need to be processed (or that are locked by other clients)',
             )
 
-        return not current_head.items and not self._in_progress
+        return (not current_head.items and not self._in_progress) or self._queue_paused_for_migration
 
     async def get_info(self) -> RequestQueueMetadata | None:
         """Get an object containing general information about the request queue."""