[FIX] im_livechat: fix chatbot restart message display

Markup usage has been enforced in the mail module since [1].

Since the `chatbot_restart` method doesn't make use of it,
the content is escaped and the whole html structure is
printed to the DOM.

This PR fixes this issue.

[1] https://github.com/odoo/odoo/pull/111850

closes odoo/odoo#122251

X-original-commit: 4909bdfbb0354310f3e6d21e1ecc7177b74b34bc
Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

addons/im_livechat/models/discuss_channel.py

@@ -236,4 +236,5 @@ class DiscussChannel(models.Model):
 
         return self._chatbot_post_message(
             chatbot_script,
-            '<div class="o_mail_notification">%s</div>' % _('Restarting conversation...'))
+            Markup('<div class="o_mail_notification">%s</div>') % _('Restarting conversation...'),
+        )