[FIX] l10n_ar_account_tax_settlement: arreglar txt ret iva sufridas

Task: 31418
El nro de comprobante pasa a ser el nro de certificado y no el nro de orden de pago

l10n_ar_account_tax_settlement/models/account_journal.py

@@ -1370,7 +1370,7 @@ def retenciones_iva_files_values(self, move_lines):
                 content += fields.Date.from_string(payment.payment_date).strftime('%d/%m/%Y')
 
                 # número comprobante (long 16)
-                content += re.sub('[^0-9\.-]', '', payment.move_name)[1:].ljust(16)
+                content += re.sub('[^0-9\.]', '', payment.withholding_number).ljust(16)
 
                 # importe retención (long 16)
                 content += '%16.2f' % payment.amount