Remove project migration spec from reliable bucket

What does this MR do?

api/1_manage/migration/gitlab_migration_project_spec.rb inconsistently fails due to a Move ProcessScanResultPolicyWorker for multiple... (#403001 - closed), see #402400 (comment 1332629771) for more details.

The MR removes gitlab_migration_project_spec from reliable bucket to reduce issues with deployments while investigation and fix for the bug is in work.

E2E Test Failure issue(s)

• Failure in api/1_manage/migration/gitlab_migrat... (#402400 - closed) -> Move ProcessScanResultPolicyWorker for multiple... (#403001 - closed)

Check-list

• General code guidelines check-list
  • Code review guidelines
  • Style guides
• Quarantine test check-list
  • Follow the Quarantining Tests guide.
  • Confirm the test has a quarantine: tag with the specified quarantine type.
  • Note if the test should be quarantined for a specific environment.
  • (Optionally) In case of an emergency (e.g. blocked deployments), consider adding labels to pick into auto-deploy (Pick into auto-deploy priority1 severity1).
• Dequarantine test check-list
  • Follow the Dequarantining Tests guide.
  • Confirm the test consistently passes on the target GitLab environment(s).
• To ensure a faster turnaround, ask in the #quality_maintainers Slack channel for someone to review and merge the merge request, rather than assigning it directly.