[FIX] l10n_it_edi: Non EU VAT fix

Non EU vendor bills are sent to the Tax Agency as self-invoices,
so the partner actually is the seller, but the same checks on the
VAT must apply as it was the buyer.

Task: https://www.odoo.com/web#id=3010849&model=project.task


opw-3010849

closes odoo/odoo#104779

Signed-off-by: Josse Colpaert <jco@odoo.com>