fix: Dont set `idx` while adding WO items to Stock Entry

- `idx` must be computed by base document's `self.append()` function, so do not set it
diff --git a/erpnext/stock/doctype/stock_entry/stock_entry.py b/erpnext/stock/doctype/stock_entry/stock_entry.py
index 99cf4de..26d59fd 100644
--- a/erpnext/stock/doctype/stock_entry/stock_entry.py
+++ b/erpnext/stock/doctype/stock_entry/stock_entry.py
@@ -1603,8 +1603,11 @@
 			se_child.is_scrap_item = item_row.get("is_scrap_item", 0)
 			se_child.is_process_loss = item_row.get("is_process_loss", 0)
 
-			for field in ["idx", "po_detail", "original_item", "expense_account",
-				"description", "item_name", "serial_no", "batch_no", "allow_zero_valuation_rate"]:
+			for field in [
+				"po_detail", "original_item", "expense_account",
+				"description", "item_name", "serial_no",
+				"batch_no", "allow_zero_valuation_rate"
+			]:
 				if item_row.get(field):
 					se_child.set(field, item_row.get(field))