feat: added stub for integration test

Author: hahnandrew

packages/test/amplify_integration_test/lib/src/stubs/amplify_auth_cognito_stub.dart

@@ -368,6 +368,13 @@ class AmplifyAuthCognitoStub extends AuthPluginInterface
     );
   }
 
+  @override
+  Future<AuthDevice> fetchCurrentDevice() async {
+    throw UnimplementedError(
+      'fetchCurrentDevice is not implemented.',
+    );
+  }
+
   @override
   Future<void> forgetDevice([AuthDevice? device]) async {
     throw UnimplementedError(
@@ -391,7 +398,6 @@ class AmplifyAuthCognitoStub extends AuthPluginInterface
 }
 
 class MockCognitoUser {
-
   factory MockCognitoUser({
     required String username,
     required String password,