Fix/pricing update fixes (#5275)

* fix for merging line items and quantity prices

* add changeset

* fix draft order unit_price calculation

* update test to reflect only quantity change

* fix unit tests

* update conditional

integration-tests/helpers/draft-order-seeder.js

@@ -92,7 +92,7 @@ module.exports = async (dataSource, data = {}) => {
     id: "test-variant",
     title: "test variant",
     product_id: "test-product",
-    inventory_quantity: 1,
+    inventory_quantity: 2,
     options: [
       {
         option_id: "test-option",