Refactor inbox_block_script library.

Closes #3491252

js/private_message_inbox_block.js

@@ -88,7 +88,9 @@
         Drupal.PrivateMessageUtils.parseHTML(threadsHtml).childNodes;
 
       newNodes.forEach((node) => {
-        const appendedElement = this.container.appendChild(node.cloneNode(true));
+        const appendedElement = this.container.appendChild(
+          node.cloneNode(true),
+        );
 
         Drupal.attachBehaviors(appendedElement);
         Drupal.PrivateMessageSlide.toggleSlide(appendedElement, true);