Prepares semantics_update_test for upcoming heading level changes (#149671)

The pr https://github.com/flutter/engine/pull/41435 adds a new property into updateNode. 

The pr migrate the method in framework first to unblock the engine pr

packages/flutter/test/semantics/semantics_update_test.dart

@@ -212,6 +212,7 @@ class SemanticsUpdateBuilderSpy extends Fake implements ui.SemanticsUpdateBuilde
     required Int32List childrenInTraversalOrder,
     required Int32List childrenInHitTestOrder,
     required Int32List additionalActions,
+    int headingLevel = 0,
   }) {
     // Makes sure we don't send the same id twice.
     assert(!observations.containsKey(id));