WIP: E2E test: exclude codeowner notifications

What does this MR do?

Code owners were getting too many notifications when automatically assigned as approvers (https://gitlab.com/gitlab-org/gitlab-ee/issues/8396). https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/8466 fixes this.

This MR updates the end-to-end test to check that code owners aren't subscribed to notifications and don't get todos.

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/8396

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?