Quarantine stale mde test

What does this MR do?

Quarantines specs/features/browser_ui/1_manage/login/maintain_login_mixed_env_spec.rb.

This spec is stale due to refactorings in our approach to mixed deployment environment specific tests. Technically, the fix will be ready in less than 24 hours, but it has a dependency on an environment change coming in the next day.

E2E Test Failure issue(s)

Related to: #344213 (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).