[FIX] sale: invalid payment link

Since bd76e9d6, if the partner set on the SO is different than the invoicing partner set on the same SO, the generated payment link won't work, as the access_token is generated based on the `partner_id`, while verified based on the `partner_invoice_id` SO field.

This commit makes sure the `access_token` is correctly generated with the invoicing partner.

opw-3328772

closes odoo/odoo#121555

Signed-off-by: Victor Feyens (vfe) <vfe@odoo.com>