fix: Post--by-start-user class not working (#3356)

framework/core/js/src/forum/components/Post.tsx

@@ -132,7 +132,7 @@ export default abstract class Post<CustomAttrs extends IPostAttrs = IPostAttrs>
       classes.push('Post--by-actor');
     }
 
-    if (user && user?.id() === discussion.attribute('startUserId')) {
+    if (user && user === discussion.user()) {
       classes.push('Post--by-start-user');
     }
 

framework/core/src/Api/Controller/ShowDiscussionController.php

@@ -48,6 +48,7 @@ class ShowDiscussionController extends AbstractShowController
      * {@inheritdoc}
      */
     public $include = [
+        'user',
         'posts',
         'posts.discussion',
         'posts.user',