[FIX] im_livechat: do not allow message edition

Before this commit, message edition was available when
pressing the arrow up key. This was a mistake since the
message edition route is not available yet for livechat
visitors. This PR fixes this issue.

closes odoo/odoo#133815

X-original-commit: ab7e70e809b3c7fa5044139582bd09a9e94ee377
Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

addons/im_livechat/static/src/embed/core/message_model_patch.js

@@ -24,4 +24,8 @@ patch(Message.prototype, {
         }
         return !this.author || this.author?.id === session.livechatData.options.current_partner_id;
     },
+
+    get editable() {
+        return this.originThread.type !== "livechat" && this._super();
+    },
 });