[FIX] account_edi_ubl_cii: fix partner creation during import

If a partner in the imported invoice does not exist, we create one on the fly. However, the partner is created without a country and `_run_vat_test` doesn't check it properly in 15.0, and fails in later versions, where we try to get the country code from the country we pass from `_import_retrieve_and_fill_partner`, which is `False`.

This commit retrieves the country from the imported invoice to create the partner and passes the object instead of the `country_code` string to `_run_vat_test`

closes odoo/odoo#122077

Signed-off-by: Laurent Smet <las@odoo.com>