Quarantine related_merge_requests_spec.js for a single assignee

What does this MR do and why?

This MR quarantines spec/frontend/issues/related_merge_requests/components/related_merge_requests_spec.js until the root cause is discovered and resolved.

Related to #387789 (closed).

See also !108641 (merged).

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.