Quarantine content_editor_spec due to progressive feature flag rollout

What does this MR do?

Quarantines qa/specs/features/browser_ui/3_create/wiki/content_editor_spec.rb:19 | Feature flag wiki_switch_between_content_editor_raw_markdown

Choosing to quarantine as this will create an unknown amount of noise in both staging and production due to there being a progressive rollout of the feature. Until the timing is known, for the rollout, it's undecided whether to refactor for rollout, so deciding to quarantine. We can then iterate once we have more information.

E2E Test Failure issue(s)

Related to #346149 (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).
• 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.