[FIX] website_sale: send extra step as public user

The extra informations not on the sale.order models were sent before
13.0 with the superuser user. In 13.0 with the change of `sudo` and
`with_user` behavior, we were now in superuser mode but not with the
superuser so the mail would error (no from address) and the sale order
would error.

With this changeset, we get back to the pre-13 behavior.

opw-2116346
closes #39730

Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>