Refactor tests to use `let_it_be` for user_sets_approvers_spec.rb
<!--IssueSummary start-->
<details>
<summary>
Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards.
</summary>
- [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=321318)
</details>
<!--IssueSummary end-->
The following discussion from !53781 should be addressed:
- [ ] @nicolasdular started a [discussion](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/53781#note_507135981): (+1 comment)
> This is backend related, but it would be cool to refactor these tests at some point and introduce `let_it_be` - however, nothing we should be concerned for this MR
issue