feat: added totals tests for end 2 end RMA flow (#8906)

what:

I've added some specs and comments in the specs for where I think totals are incorrect. 

Lets get this test merged in as the status quo and proceed to fix these issues one by one.

Additionally, this also removes the temporary_difference as its not something we use. 

RESOLVES CC-346

Co-authored-by: Carlos R. L. Rodrigues <37986729+carlos-r-l-rodrigues@users.noreply.github.com>

integration-tests/http/__tests__/fixtures/order.ts

@@ -28,9 +28,7 @@ export async function createOrderSeeder({ api }) {
   const inventoryItem = (
     await api.post(
       `/admin/inventory-items`,
-      {
-        sku: `12345-${stockLocation.id}`,
-      },
+      { sku: "test-variant" },
       adminHeaders
     )
   ).data.inventory_item
@@ -70,6 +68,7 @@ export async function createOrderSeeder({ api }) {
         variants: [
           {
             title: "Test variant",
+            sku: "test-variant",
             inventory_items: [
               {
                 inventory_item_id: inventoryItem.id,