[FIX] website_sale: fix authorized message

Field `auth_msg` never existed, this is an uncaught mistake. This commit
removes its usage and displays the fallback message to avoid runtime
error.

Closes #31903

Signed-off-by: Toufik Benjaa (tbe) <tbe@odoo.com>


Co-authored-by: Marius Stedjan <marius@stedjan.com>