purchase_advance_payment: pre-fill Ref. from purchase partner_ref

🤖 assisted by claude

odoo-bringout-oca-purchase-workflow-purchase_advance_payment/purchase_advance_payment/wizard/purchase_advance_payment_wizard.py

@@ -126,6 +126,8 @@ class AccountVoucherWizardPurchase(models.TransientModel):
             )
             .id
         )
+        if purchase.partner_ref:
+            res["payment_ref"] = purchase.partner_ref
         return res
 
     @api.depends("journal_id", "date", "amount_advance", "journal_currency_id")