Fix indentation in flutter integration test example (#9437)

## Presubmit checklist

- [x] This PR doesn’t contain automatically generated corrections
(Grammarly or similar).
- [x] This PR follows the [Google Developer Documentation Style
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- [x] This PR uses [semantic line
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---------

Co-authored-by: Parker Lougheed <parlough@gmail.com>

examples/testing/integration_tests/how_to/integration_test/counter_test.dart

@@ -1,10 +1,13 @@
+// #docregion initial
 import 'package:flutter_test/flutter_test.dart';
 import 'package:how_to/main.dart';
 import 'package:integration_test/integration_test.dart';
 
 void main() {
+  // #enddocregion initial
   IntegrationTestWidgetsFlutterBinding.ensureInitialized(); // NEW
 
+  // #docregion initial
   testWidgets('tap on the floating action button, verify counter',
       (tester) async {
     // Load app widget.
@@ -27,3 +30,4 @@ void main() {
     expect(find.text('1'), findsOneWidget);
   });
 }
+// #enddocregion initial

src/testing/integration-tests/index.md

@@ -88,14 +88,14 @@ Changed 9 dependencies!
 In your project, create a new directory
 `integration_test` with a new file, `<name>_test.dart`:
 
-<?code-excerpt "integration_test/counter_test.dart" replace="/IntegrationTestWidgetsFlutterBinding\.ensureInitialized\(\); \/\/ NEW\n\n//g"?>
+<?code-excerpt "integration_test/counter_test.dart (initial)" plaster="none"?>
 ```dart
 import 'package:flutter_test/flutter_test.dart';
 import 'package:how_to/main.dart';
 import 'package:integration_test/integration_test.dart';
 
 void main() {
-    testWidgets('tap on the floating action button, verify counter',
+  testWidgets('tap on the floating action button, verify counter',
       (tester) async {
     // Load app widget.
     await tester.pumpWidget(const MyApp());