Fix to clear SO Allocations on receipt of Return Order Line Item (#6117)

* Added stock_item.clearAllocations() to order.models.py

* Update models.py ReturnOrder clear allocations on line receipt

InvenTree/order/models.py

@@ -1926,6 +1926,7 @@ class ReturnOrder(TotalPriceMixin, Order):
         stock_item.customer = None
         stock_item.sales_order = None
         stock_item.save(add_note=False)
+        stock_item.clearAllocations()
 
         # Add a tracking entry to the StockItem
         stock_item.add_tracking_entry(