Disables test failing due to new semantics flag. (#65194)

This change disables a failing test prevent PR #20385 from merging.

packages/flutter_test/test/matchers_test.dart

@@ -618,7 +618,7 @@ void main() {
          hasDismissAction: true,
          customActions: <CustomSemanticsAction>[action],
       ));
-    });
+    }, skip: true); // TODO(abrusher): Enable once engine PR #20385 lands.
 
     testWidgets('Can match child semantics', (WidgetTester tester) async {
       final SemanticsHandle handle = tester.ensureSemantics();