Classify foreign ISR withholdings separately

Assign payments to non-residents to the dedicated ISREXT group in both localization datasets and tax rules. Add regression checks for national and foreign ISR groups.

ir.py

@@ -2,11 +2,9 @@
 # this repository contains the full copyright notices and license terms.
 
 from sql import Table
-
 from trytond.pool import PoolMeta
 from trytond.transaction import Transaction
 
-
 LEGACY_OBSOLETE_IDS = {
     'do_tax_itbis_8_compra', 'do_tax_itbis_8_venta',
     'do_tax_itbis_9_compra', 'do_tax_itbis_9_venta',