Update app tests for M3 (#130792)

This PR updates unit tests from `app_test.dart` for M3 migration.

More info in https://github.com/flutter/flutter/issues/127064

The diff is somewhat misleading because third test in the original code is now the fourth in the updated one, but because they were very similar git diff does not reflect this swap.

And also, first test is M2 only and last one M3 only.

packages/flutter/test/material/app_test.dart

@@ -979,7 +979,7 @@ void main() {
     expect(themeAfterBrightnessChange!.brightness, Brightness.dark);
   });
 
-  testWidgets('MaterialApp provides default overscroll color', (WidgetTester tester) async {
+  testWidgets('Material2 - MaterialApp provides default overscroll color', (WidgetTester tester) async {
     Future<void> slowDrag(WidgetTester tester, Offset start, Offset offset) async {
       final TestGesture gesture = await tester.startGesture(start);
       for (int index = 0; index < 10; index += 1) {
@@ -1262,7 +1262,7 @@ void main() {
     expect(scrollBehavior.getScrollPhysics(capturedContext).runtimeType, NeverScrollableScrollPhysics);
   });
 
-  testWidgets('ScrollBehavior default android overscroll indicator', (WidgetTester tester) async {
+  testWidgets('Material2 - ScrollBehavior default android overscroll indicator', (WidgetTester tester) async {
     await tester.pumpWidget(MaterialApp(
       theme: ThemeData(useMaterial3: false),
       scrollBehavior: const MaterialScrollBehavior(),
@@ -1281,9 +1281,10 @@ void main() {
     expect(find.byType(GlowingOverscrollIndicator), findsOneWidget);
   }, variant: TargetPlatformVariant.only(TargetPlatform.android));
 
-  testWidgets('ScrollBehavior stretch android overscroll indicator', (WidgetTester tester) async {
+  testWidgets('Material3 - ScrollBehavior default android overscroll indicator', (WidgetTester tester) async {
     await tester.pumpWidget(MaterialApp(
-      scrollBehavior: const MaterialScrollBehavior(androidOverscrollIndicator: AndroidOverscrollIndicator.stretch),
+      theme: ThemeData(useMaterial3: true),
+      scrollBehavior: const MaterialScrollBehavior(),
       home: ListView(
         children: const <Widget>[
           SizedBox(
@@ -1299,9 +1300,9 @@ void main() {
     expect(find.byType(GlowingOverscrollIndicator), findsNothing);
   }, variant: TargetPlatformVariant.only(TargetPlatform.android));
 
-  testWidgets('ScrollBehavior stretch android overscroll indicator via useMaterial3 flag', (WidgetTester tester) async {
+  testWidgets('ScrollBehavior stretch android overscroll indicator', (WidgetTester tester) async {
     await tester.pumpWidget(MaterialApp(
-      theme: ThemeData(useMaterial3: true),
+      scrollBehavior: const MaterialScrollBehavior(androidOverscrollIndicator: AndroidOverscrollIndicator.stretch),
       home: ListView(
         children: const <Widget>[
           SizedBox(
@@ -1356,8 +1357,7 @@ void main() {
     expect(find.byType(GlowingOverscrollIndicator), findsNothing);
   }, variant: TargetPlatformVariant.only(TargetPlatform.android));
 
-  testWidgets(
-    'ListView clip behavior updates overscroll indicator clip behavior', (WidgetTester tester) async {
+  testWidgets('Material3 - ListView clip behavior updates overscroll indicator clip behavior', (WidgetTester tester) async {
     Widget buildFrame(Clip clipBehavior) {
       return MaterialApp(
         theme: ThemeData(useMaterial3: true),