Add `goleak` detection to workhorse tests
<!--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=468090) </details> <!--IssueSummary end--> Updating the workhorse tests to look for [`goleak`](https://github.com/uber-go/goleak)s will ideally help us detect Goroutine leaks during development (and not in production 🙏). Related: https://gitlab.com/gitlab-com/gl-infra/capacity-planning-trackers/gitlab-com/-/issues/1796#note_1956967107 <!-- template sourced from https://gitlab.com/gitlab-org/gitlab/-/blob/master/.gitlab/issue_templates/Default.md -->
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