fix: use worker_tasks list instead of non-existent worker_task attribute

tests/unit/test_background_loader_service.py

@@ -36,6 +36,7 @@ def mock_anime_service():
     """Mock AnimeService."""
     service = AsyncMock()
     service.sync_episodes_to_db = AsyncMock()
+    service.sync_single_series_after_scan = AsyncMock()
     return service
 
 
@@ -600,7 +601,7 @@ class TestScanMissingEpisodes:
             await background_loader_service._scan_missing_episodes(task, mock_db)
         
         assert task.progress["episodes"] is True
-        background_loader_service.anime_service.sync_episodes_to_db.assert_called_once_with("test")
+        background_loader_service.anime_service.sync_single_series_after_scan.assert_called_once_with("test")
     
     @pytest.mark.asyncio
     async def test_scan_missing_episodes_no_scanner(self, background_loader_service):