[FIX] website_forum: update flagged posts count

When flagging a post, moderators should see the flagged moderation queue
counter appear/increment.

We renamed the span in 21531bd9 and forgot to update this reference.

Task-3349373

closes odoo/odoo#151512

X-original-commit: 720d7b53e7d1a0944415a6c668f4eb3ba527dac8
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>
Signed-off-by: Florian Charlier (flch) <flch@odoo.com>

addons/website_forum/static/src/js/website_forum.js

@@ -346,7 +346,7 @@ publicWidget.registry.websiteForum = publicWidget.Widget.extend({
             } else if (data.success) {
                 const child = elem.firstElementChild;
                 if (data.success === 'post_flagged_moderator') {
-                    const countFlaggedPosts = this.el.querySelector('#count_flagged_posts');
+                    const countFlaggedPosts = this.el.querySelector('#count_posts_queue_flagged');
                     elem.innerText = _t(' Flagged');
                     elem.prepend(child);
                     if (countFlaggedPosts) {