[FIX] purchase: fix bill ref replaced by PO ref when using auto complete

Issue

	- Accounting & Purchase
	- Create a PO for wood corner
	- Create a bill for wood corner, add a ref
	  and auto complete with the previous PO

	The ref is replaced by the PO's one

Cause

	In purchase account_invoice _onchange_purchase_auto_complete
	we update all the bill values with the PO values including
	the PO ref (empty or not)

Solution

	Exclude the ref of fields to be updated

OPW-2313418

closes odoo/odoo#55560

X-original-commit: ae0c3b600403a21a196e51ce88fa6b25990f2b64
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

addons/purchase/models/account_invoice.py

@@ -45,6 +45,7 @@ class AccountMove(models.Model):
 
         # Copy data from PO
         invoice_vals = self.purchase_id.with_company(self.purchase_id.company_id)._prepare_invoice()
+        del invoice_vals['ref']
         self.update(invoice_vals)
 
         # Copy purchase lines.