De quarantine merge_merge_request_from_fork_spec.rb

What does this MR do?

Test has been failing with errors such as #343801 (closed).
Investigation showed that gitlab-qa-forker was not activated in production #343801 (comment 957469134) That has been resolved and the user is now activated and can login.

E2E Test Failure issue(s)

https://gitlab.com/gitlab-org/gitlab/-/quality/test_cases/347818

Check-list

• General code guidelines check-list

  • Code review guidelines
  • Style guides

• Dequarantine test check-list

  • Follow the Dequarantining Tests guide.
  • Confirm the test consistently passes on the target GitLab environment(s).
    • (Optionally) Trigger a manual GitLab-QA pipeline against a specific GitLab environment using the RELEASE variable from the package-and-qa job of the current merge request.
    • https://ops.gitlab.net/gitlab-org/quality/production/-/pipelines/1264617
      • https://ops.gitlab.net/gitlab-org/quality/production/-/jobs/7378246
    • https://ops.gitlab.net/gitlab-org/quality/production/-/pipelines/1264672
      • https://ops.gitlab.net/gitlab-org/quality/production/-/jobs/7378619
    • https://ops.gitlab.net/gitlab-org/quality/production/-/pipelines/1264723
      • https://ops.gitlab.net/gitlab-org/quality/production/-/jobs/7379081

• To ensure a faster turnaround, ask in the #quality Slack channel for someone to review and merge the merge request, rather than assigning it directly.