fix: calculate `stock_value_diff`

`d.item_tax_amount` is already in base currency.
diff --git a/erpnext/stock/doctype/purchase_receipt/purchase_receipt.py b/erpnext/stock/doctype/purchase_receipt/purchase_receipt.py
index c9fe7d2..1e2d8eb 100644
--- a/erpnext/stock/doctype/purchase_receipt/purchase_receipt.py
+++ b/erpnext/stock/doctype/purchase_receipt/purchase_receipt.py
@@ -686,9 +686,7 @@
 						)
 
 					stock_value_diff = (
-						flt(d.base_net_amount)
-						+ flt(d.item_tax_amount / self.conversion_rate)
-						+ flt(d.landed_cost_voucher_amount)
+						flt(d.base_net_amount) + flt(d.item_tax_amount) + flt(d.landed_cost_voucher_amount)
 					)
 				elif warehouse_account.get(d.warehouse):
 					stock_value_diff = get_stock_value_difference(self.name, d.name, d.warehouse)