Add test for scaffold_state.show_bottom_sheet.0.dart (#152731)

Contributes to https://github.com/flutter/flutter/issues/130459

It adds a test for
- `examples/api/lib/material/scaffold/scaffold_state.show_bottom_sheet.0.dart`

dev/bots/check_code_samples.dart

@@ -320,7 +320,6 @@ final Set<String> _knownMissingTests = <String>{
   'examples/api/test/material/platform_menu_bar/platform_menu_bar.0_test.dart',
   'examples/api/test/material/flexible_space_bar/flexible_space_bar.0_test.dart',
   'examples/api/test/material/selection_area/selection_area.0_test.dart',
-  'examples/api/test/material/scaffold/scaffold_state.show_bottom_sheet.0_test.dart',
   'examples/api/test/material/scaffold/scaffold_messenger_state.show_material_banner.0_test.dart',
   'examples/api/test/material/scaffold/scaffold_messenger_state.show_snack_bar.0_test.dart',
   'examples/api/test/material/app_bar/sliver_app_bar.2_test.dart',

examples/api/test/material/scaffold/scaffold_state.show_bottom_sheet.0_test.dart

@@ -0,0 +1,26 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:flutter_api_samples/material/scaffold/scaffold_state.show_bottom_sheet.0.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('The button should show a bottom sheet when pressed', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.ShowBottomSheetExampleApp(),
+    );
+
+    expect(find.widgetWithText(AppBar, 'ScaffoldState Sample'), findsOne);
+    await tester.tap(find.widgetWithText(ElevatedButton, 'showBottomSheet'));
+    await tester.pumpAndSettle();
+
+    expect(find.widgetWithText(BottomSheet, 'BottomSheet'), findsOne);
+
+    await tester.tap(find.widgetWithText(ElevatedButton, 'Close BottomSheet'));
+    await tester.pumpAndSettle();
+
+    expect(find.widgetWithText(BottomSheet, 'BottomSheet'), findsNothing);
+  });
+}