[FIX] mail: Don't log unhandled notification

The `mail` module logs bus notifications it does not handle. However, some
notifications are not meant to be handled by `mail` and it's perfectly fine.

This commit removes the log to avoid useless noise in the console.

closes odoo/odoo#66661

Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>