Quarantine import E2E specs

What does this MR do?

Quarantining GitHub import E2E specs to reduce pipeline noise while potential fix is being worked in !111607 (merged)

E2E Test Failure issue(s)

• Failure in api/1_manage/import/import_github_re... (#391228 - closed)
• Failure in browser_ui/1_manage/import/import_gi... (#391230 - 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.