Fix test should create simple product without sku SALEOR_2806

[szczecha]

I want to merge this change because it fixes the test and adds mutation to create variant stock

PR intended to be tested with API branch:

Screenshots

Pull Request Checklist

1. This code contains UI changes
2. All visible strings are translated with proper context including data-formatting
3. Attributes [data-test-id] are added for new elements
4. Changes are mentioned in the changelog
5. The changes are tested in different browsers and in light/dark mode

Test environment config

API_URI=https://automation-dashboard.staging.saleor.cloud/graphql/
MARKETPLACE_URL=https://apps.saleor.io
SALEOR_APPS_ENDPOINT=https://apps.saleor.io/api/saleor-apps

Do you want to run more stable tests?

To run all tests, just select the stable checkbox. To speed up tests, increase the number of containers. Tests will be re-run only when the "run e2e" label is added.

1. stable
2. giftCard
3. category
4. collection
5. attribute
6. productType
7. shipping
8. customer
9. permissions
10. menuNavigation
11. pages
12. sales
13. vouchers
14. homePage
15. login
16. orders
17. products
18. app
19. plugins
20. translations
21. navigation
22. variants

CONTAINERS=1