[FIX] l10n_it_edi: self-invoices require fiscal regime RF18

When the seller is foreign, the Fiscal Regime of the seller must
be set to 'RF18', as per:
https://www.fattura24.com/manuale/altri-documenti/autofattura-fornitori/

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

closes odoo/odoo#104903

X-original-commit: 07747178a230071f9ca3cd7202ad571f80a330c0
Signed-off-by: Josse Colpaert <jco@odoo.com>
Signed-off-by: Paolo Gatti (pgi) <pgi@odoo.com>

addons/l10n_it_edi/models/account_invoice.py

@@ -253,7 +253,7 @@ class AccountMove(models.Model):
             'document_total': document_total,
             'representative': company.l10n_it_tax_representative_partner_id,
             'codice_destinatario': codice_destinatario,
-            'regime_fiscale': company.l10n_it_tax_system if not is_self_invoice else 'RF01',
+            'regime_fiscale': company.l10n_it_tax_system if not is_self_invoice else 'RF18',
             'is_self_invoice': is_self_invoice,
             'partner_bank': self.partner_bank_id,
             'format_date': format_date,

addons/l10n_it_edi/tests/expected_xmls/reverse_charge_bill.xml

@@ -20,7 +20,7 @@
                 <Anagrafica>
                     <Denominazione>Alessi</Denominazione>
                 </Anagrafica>
-                <RegimeFiscale>RF01</RegimeFiscale>
+                <RegimeFiscale>RF18</RegimeFiscale>
             </DatiAnagrafici>
             <Sede>
                 <Indirizzo>Avenue Test rue </Indirizzo>