MC-16607: Fix Unrelated Static Test Failures

- update to correct plugin's class
- clarify where plugin is used

Author: anthoula

app/code/Magento/PageBuilder/Plugin/Filter/CustomVarTemplate.php

@@ -30,14 +30,14 @@ public function __construct(
     }
 
     /**
-     * Determine if custom variable directive's return value needs to be escaped and do so if true
+     * Determine if custom variable within a Page Builder CMS Block directive's return value needs to be escaped
      *
-     * @param \Magento\Framework\Filter\Template $subject
+     * @param \Magento\Email\Model\Template\Filter $subject
      * @param string $result
      * @return string
      */
     public function afterCustomvarDirective(
-        \Magento\Framework\Filter\Template $subject,
+        \Magento\Email\Model\Template\Filter $subject,
         $result
     ) {
         // Determine the need to escape the return value of observed method.

app/code/Magento/PageBuilder/etc/frontend/di.xml

@@ -11,6 +11,8 @@
     </type>
     <type name="Magento\Framework\Filter\Template">
         <plugin name="convertBackgroundImages" type="Magento\PageBuilder\Plugin\Filter\TemplatePlugin"/>
+    </type>
+    <type name="Magento\Email\Model\Template\Filter">
         <plugin name="escapeCustomVarDirectives" type="Magento\PageBuilder\Plugin\Filter\CustomVarTemplate"/>
     </type>
 </config>