Fix intermittent failures in playground/server-origin

Editor assessment

Typing a flaky-test repair as `test` is exactly right, and the scope is embedded in the subject via the path-like `playground/server-origin`, which is informative even if a formal `test(playground)` scope would look tidier. The subject is lowercase, imperative, and comfortably short. 'Intermittent failures' is a useful keyword for anyone searching history for flakiness, though a body describing the root cause — timing, ordering, shared state — would convert this from a pointer to an explanation. Minor, but such notes are invaluable when the same flake resurfaces later.