[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