Update SemanticsUpdateBuilderSpy for the conversion of SemanticsUpdateBuilder into a base class (#126570)

See flutter/flutter#123756

Author: jason-simmons

packages/flutter/test/semantics/semantics_update_test.dart

@@ -175,7 +175,9 @@ class SemanticsUpdateTestBinding extends AutomatedTestWidgetsFlutterBinding {
   }
 }
 
-class SemanticsUpdateBuilderSpy extends ui.SemanticsUpdateBuilder {
+class SemanticsUpdateBuilderSpy extends Fake implements ui.SemanticsUpdateBuilder {
+  final SemanticsUpdateBuilder _builder = ui.SemanticsUpdateBuilder();
+
   static Map<int, SemanticsNodeUpdateObservation> observations = <int, SemanticsNodeUpdateObservation>{};
 
   @override
@@ -249,6 +251,13 @@ class SemanticsUpdateBuilderSpy extends ui.SemanticsUpdateBuilder {
       additionalActions: additionalActions,
     );
   }
+
+  @override
+  void updateCustomAction({required int id, String? label, String? hint, int overrideId = -1}) =>
+    _builder.updateCustomAction(id: id, label: label, hint: hint, overrideId: overrideId);
+
+  @override
+  ui.SemanticsUpdate build() => _builder.build();
 }
 
 class SemanticsNodeUpdateObservation {