Fix sample code (#67940)

packages/flutter/lib/src/widgets/nested_scroll_view.dart

@@ -61,7 +61,7 @@ typedef NestedScrollViewHeaderSliversBuilder = List<Widget> Function(BuildContex
 /// (those inside the [TabBarView], hooking them together so that they appear,
 /// to the user, as one coherent scroll view.
 ///
-/// {@tool sample --template=stateless_widget_scaffold}
+/// {@tool sample --template=stateless_widget_material}
 ///
 /// This example shows a [NestedScrollView] whose header is the combination of a
 /// [TabBar] in a [SliverAppBar] and whose body is a [TabBarView]. It uses a
@@ -76,7 +76,8 @@ typedef NestedScrollViewHeaderSliversBuilder = List<Widget> Function(BuildContex
 ///   final List<String> _tabs = ['Tab 1', 'Tab 2'];
 ///   return DefaultTabController(
 ///     length: _tabs.length, // This is the number of tabs.
-///     child: NestedScrollView(
+///     child: Scaffold(
+///       body: NestedScrollView(
 ///         headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
 ///           // These are the slivers that show up in the "outer" scroll view.
 ///           return <Widget>[
@@ -173,6 +174,7 @@ typedef NestedScrollViewHeaderSliversBuilder = List<Widget> Function(BuildContex
 ///           }).toList(),
 ///         ),
 ///       ),
+///     ),
 ///   );
 /// }
 /// ```