This fix adjusts the mail chatter test setup so edited messages keep the expected layout when their styling changes. It helps ensure message lists continue to scroll correctly, reducing the risk of frustrating navigation issues in customer communications.

Lack of "p" tag in the message body in chatter test changes the size of message and its position relative to the view.

Task-2664848

Related to this [PR](https://github.com/odoo/odoo/pull/117896)