fix: _validate_subgraph bug

apps/mtm/models.py

@@ -283,7 +283,7 @@ class RoutePack(CommonADModel):
             }
         return result
 
-    def _validate_subgraph(materials, graph, final_id):
+    def _validate_subgraph(self, materials, graph, final_id):
         """校验单个子图的有效性并返回层级结构"""
         errors = []
         levels = {}