Rails5: fix flaky spec

What does this MR do?

Fix a flaky rails5 spec that happened in some of the latest scheduled pipelines:

• https://gitlab.com/gitlab-org/gitlab-ce/-/jobs/85548867
• https://gitlab.com/gitlab-org/gitlab-ce/-/jobs/85548835
• https://gitlab.com/gitlab-org/gitlab-ce/-/jobs/85553861

I can't reproduce it locally, but this fix is working. I already retried the pipeline 3 times and it has not failed.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

rails5 upgrade

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conforms to the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?