Quarantine flaky test due to master-broken incident

What does this MR do and why?

Quarantines the spec ./ee/spec/features/registrations/saas/invite_flow_spec.rb:23 for being flaky and causing a master-broken incident.

Screenshots or screen recordings

No visible change

How to set up and validate locally

1. Run spec ./ee/spec/features/registrations/saas/invite_flow_spec.rb or check pipeline

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #423547 (closed)