[FIX] account_edi_ubl(_bis3): OrderReference should refer to the PO of the customer

According to https://docs.peppol.eu/poacc/billing/3.0/syntax/ubl-invoice/cac-OrderReference/


the cbc:ID in the Order Reference should be the PO number of the customer.

closes odoo/odoo#84988

X-original-commit: cd414536
Signed-off-by: Laurent Smet <las@odoo.com>
Signed-off-by: William André (wan) <wan@odoo.com>