magento-test/app/code/Magento/SalesInventory/etc/di.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\Sales\Model\Order\CreditmemoDocumentFactory">
        <plugin name="sales_inventory_creditmemo_item_set_back_to_stock" type="Magento\SalesInventory\Model\Plugin\Order\CreditmemoDocumentFactoryPlugin"/>
    </type>
    <type name="Magento\Sales\Model\Order\Validation\RefundOrderInterface">
        <plugin name="refundOrderValidationAfter" type="Magento\SalesInventory\Model\Plugin\Order\Validation\OrderRefundCreationArguments"/>
    </type>
    <type name="Magento\Sales\Model\Order\Validation\RefundInvoiceInterface">
        <plugin name="refundInvoiceValidationAfter" type="Magento\SalesInventory\Model\Plugin\Order\Validation\InvoiceRefundCreationArguments"/>
    </type>
</config>