Enable Material 3 on `background_isolate_channels` (#1946)

background_isolate_channels/lib/main.dart

@@ -31,6 +31,7 @@ class MyApp extends StatelessWidget {
       title: 'Background Isolate Channels',
       theme: ThemeData(
         primarySwatch: Colors.blue,
+        useMaterial3: true,
       ),
       home: const MyHomePage(title: 'Background Isolate Channels'),
     );
@@ -124,27 +125,25 @@ class _MyHomePageState extends State<MyHomePage> {
     return Scaffold(
       appBar: AppBar(
         title: Text(widget.title),
-      ),
+        bottom: PreferredSize(
-      body: Column(
+          preferredSize: const Size.fromHeight(kToolbarHeight),
-        children: [
+          child: Padding(
-          TextField(
+            padding: const EdgeInsets.symmetric(horizontal: 8.0),
+            child: SearchBar(
+              hintText: 'Search',
               onChanged:
                   _database == null ? null : (query) => _refresh(query: query),
-            decoration: const InputDecoration(
+              trailing: const [Icon(Icons.search), SizedBox(width: 8)],
-              labelText: 'Search',
+            ),
-              suffixIcon: Icon(Icons.search),
+          ),
         ),
       ),
-          Expanded(
+      body: ListView.builder(
-            child: ListView.builder(
         itemBuilder: (context, index) {
           return ListTile(title: Text(_entries![index]));
         },
         itemCount: _entries?.length ?? 0,
       ),
-          ),
-        ],
-      ),
       floatingActionButton: FloatingActionButton(
         onPressed: _database == null ? null : _addDate,
         tooltip: 'Add',