[FIX] sale: fix type of created invoice from SO

Consider the generation of an invoice for a SO having the following lines:
quantity | unit price | taxes | subtotal
----------------------------------------
       1 |        100 |   15% |      115
       1 |       -110 |       |     -110

Previously, the invoice wrongly received the type 'out_refund' instead of 'out_invoice'. This was because the code was only considering the untaxed amount.

Closes #28259
Fixes #26726

Co-authored by pedrobaeza

addons/sale/models/sale.py

@@ -372,10 +372,11 @@ class SaleOrder(models.Model):
             raise UserError(_('There is no invoicable line.'))
 
         for invoice in invoices.values():
+            invoice.compute_taxes()
             if not invoice.invoice_line_ids:
                 raise UserError(_('There is no invoicable line.'))
             # If invoice is negative, do a refund invoice instead
-            if invoice.amount_untaxed < 0:
+            if invoice.amount_total < 0:
                 invoice.type = 'out_refund'
                 for line in invoice.invoice_line_ids:
                     line.quantity = -line.quantity