Intermittent PASS in `/html/browsers/browsing-the-web/remote-context-helper-tests/navigation-bfcache.window.html`

Probably introduced by #39421

https://github.com/servo/servo/runs/51383621063
```
OK [expected TIMEOUT] /html/browsers/browsing-the-web/remote-context-helper-tests/navigation-bfcache.window.html

    PASS [expected TIMEOUT] subtest: RemoteContextHelper navigation using BFCache
```