Added backward compatibility.

Added backward compatibility for the new orderManagementInterface dependency and made the variable $orderManagement private.

Author: AnshuMishra17

app/code/Magento/Sales/Controller/Adminhtml/Order/MassUnhold.php

@@ -21,7 +21,7 @@ class MassUnhold extends AbstractMassAction
     /**
      * @var OrderManagementInterface
      */
-    protected $orderManagement;
+    private $orderManagement;
 
     /**
      * @param Context $context
@@ -33,7 +33,7 @@ public function __construct(Context $context, Filter $filter, CollectionFactory
     {
         parent::__construct($context, $filter);
         $this->collectionFactory = $collectionFactory;
-        $this->orderManagement = $orderManagement;
+        $this->orderManagement = $orderManagement ?: \Magento\Framework\App\ObjectManager::getInstance()->get(\Magento\Sales\Api\OrderManagementInterface::class);
     }
 
     /**