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.

tax_rule_do_es_419.xml

@@ -52,7 +52,7 @@
     </record>
     <record id="do_trline_supp_ext_isr27_es_419" model="account.tax.rule.line.template">
       <field name="rule" ref="do_tax_rule_supplier_ext_es_419" />
-      <field name="group" ref="do_tax_group_isr_es_419" />
+      <field name="group" ref="do_tax_group_isr_ext_es_419" />
       <field name="tax" ref="do_tax_ret_isr_ext_27_es_419" />
       <field name="sequence" eval="10" />
     </record>
@@ -311,4 +311,4 @@
       <field name="sequence" eval="40" />
     </record>
   </data>
-</tryton>
+</tryton>