benchmarkWidgets.semanticsEnabled default false. (#35280)

In order not to break existing benchmarks.

packages/flutter_test/lib/src/widget_tester.dart

@@ -173,7 +173,7 @@ void testWidgets(
 Future<void> benchmarkWidgets(
   WidgetTesterCallback callback, {
   bool mayRunWithAsserts = false,
-  bool semanticsEnabled = true,
+  bool semanticsEnabled = false,
 }) {
   assert(() {
     if (mayRunWithAsserts)