Fixed failed static test

Author: engcom-Charlie

app/code/Magento/Indexer/Test/Unit/Controller/Adminhtml/Indexer/MassOnTheFlyTest.php

@@ -82,7 +82,7 @@ class MassOnTheFlyTest extends TestCase
     protected $indexReg;
 
     /**
-     * @return ResponseInterface
+     * @var ResponseInterface
      */
     protected $response;