fix: set correct purchase_sle in get_last_sle() (#37708)

sle_dict may look like this:
{
  'incoming': [
    {... Stock Entry ...},
    {... Purchase Receipt ...}
  ],
  'outgoing': [
    {... Stock Entry ...}
  ]
}

erpnext/stock/doctype/serial_no/serial_no.py

@@ -191,7 +191,7 @@ def get_last_sle(self, serial_no=None):
 		sle_dict = self.get_stock_ledger_entries(serial_no)
 		if sle_dict:
 			if sle_dict.get("incoming", []):
-				entries["purchase_sle"] = sle_dict["incoming"][0]
+				entries["purchase_sle"] = sle_dict["incoming"][-1]
 
 			if len(sle_dict.get("incoming", [])) - len(sle_dict.get("outgoing", [])) > 0:
 				entries["last_sle"] = sle_dict["incoming"][0]