chore: add testUrlScheme back to test (aws-amplify#5223)

Author: Jordan-Nelson

packages/auth/amplify_auth_cognito/example/integration_test/native_auth_bridge_test.dart

@@ -18,6 +18,8 @@ import 'package:http/testing.dart';
 
 import 'test_runner.dart';
 
+const testUrlScheme = 'authtest';
+
 void main() {
   testRunner.setupTests();