newsupernova/vendor/magento/module-email/etc/adminhtml/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">
    <virtualType name="Magento\Config\Model\Config\Source\Email\Template\Header" type="Magento\Config\Model\Config\Source\Email\Template">
        <arguments>
            <argument name="data" xsi:type="array">
                <item name="path" xsi:type="string">design/email/header_template</item>
            </argument>
        </arguments>
    </virtualType>
    <virtualType name="Magento\Config\Model\Config\Source\Email\Template\Footer" type="Magento\Config\Model\Config\Source\Email\Template">
        <arguments>
            <argument name="data" xsi:type="array">
                <item name="path" xsi:type="string">design/email/footer_template</item>
            </argument>
        </arguments>
    </virtualType>
</config>