Add post-submit failing test to close the tree for #94356 (#94390)

dev/devicelab/bin/tasks/flavors_test.dart

@@ -13,6 +13,10 @@ Future<void> main() async {
     await createFlavorsTest().call();
     await createIntegrationTestFlavorsTest().call();
 
-    return TaskResult.success(null);
+    // This is a test that we can use to close the tree until
+    // https://github.com/flutter/flutter/issues/74529 is addressed.
+
+    return TaskResult.failure('Failing to close the tree for https://github.com/flutter/flutter/issues/94356');
+    // return TaskResult.success(null);
   });
 }

packages/flutter_tools/test/general.shard/failing_test.dart

-// 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 '../src/common.dart';
-
-// This is a test that we can use to close the tree until
-// https://github.com/flutter/flutter/issues/74529 is addressed.
-
-void main() {
-  test('Fail unconditionally', () { // ignore: void_checks
-    fail('Failing to close the tree for https://github.com/flutter/flutter/issues/94356');
-  }); // Skip this test to re-open the tree.
-}