add friend class in op_filter

Author: peace-dove

src/cypher/execution_plan/ops/op_filter.h

@@ -24,6 +24,7 @@ namespace cypher {
 
 class OpFilter : public OpBase {
     friend class EdgeFilterPushdownExpand;
+    friend class EdgeFilterPushdownVarLenExpand;
     std::shared_ptr<lgraph::Filter> filter_;
     /* FilterState
      * Different states in which ExpandAll can be at. */