Fix strict type declaration

Author: VladimirZaets

app/code/Magento/CheckoutAgreements/Model/ResourceModel/Agreement/Grid/Collection.php

@@ -3,6 +3,7 @@
  * Copyright © Magento, Inc. All rights reserved.
  * See COPYING.txt for license details.
  */
+declare(strict_types=1);
 
 namespace Magento\CheckoutAgreements\Model\ResourceModel\Agreement\Grid;