Replace references to LinearProgressIndicator in CircularProgressIndi…

…cator example (flutter#103349)

* Replace references to LinearProgressIndicator in CircularProgressIndicator example

* Add test

* fix copyright header

examples/api/lib/material/progress_indicator/circular_progress_indicator.0.dart

@@ -61,12 +61,12 @@ class _MyStatefulWidgetState extends State<MyStatefulWidget>
           mainAxisAlignment: MainAxisAlignment.spaceEvenly,
           children: <Widget>[
             Text(
-              'Linear progress indicator with a fixed color',
+              'Circular progress indicator with a fixed color',
               style: Theme.of(context).textTheme.headline6,
             ),
             CircularProgressIndicator(
               value: controller.value,
-              semanticsLabel: 'Linear progress indicator',
+              semanticsLabel: 'Circular progress indicator',
             ),
           ],
         ),

examples/api/test/material/progress_indicator/circular_progress_indicator.0_test.dart

@@ -0,0 +1,19 @@
+// 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_api_samples/material/progress_indicator/circular_progress_indicator.0.dart'
+    as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('Finds CircularProgressIndicator', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.MyApp(),
+    );
+    expect(
+      find.bySemanticsLabel('Circular progress indicator'),
+      findsOneWidget,
+    );
+  });
+}