Intermittent timeout in /_mozilla/mozilla/websocket_connection_fail.html

The intermittent only showed up after 592 runs:
```
./mach test-wpt --release --repeat-until-unexpected /_mozilla/mozilla/websocket_connection_fail.html
...
  ▶ Unexpected subtest result in /_mozilla/mozilla/websocket_connection_fail.html:
  │ TIMEOUT [expected PASS] Untitled
  └   → Test timed out

  [592/1] No tests running.
```