Intermittent FAIL in  `/fetch/fetch-later/send-on-discard/not-send-after-abort.https.window.html`

```
OK /fetch/fetch-later/send-on-discard/not-send-after-abort.https.window.html

    FAIL [expected PASS] subtest: A discarded document does not send an already aborted fetchLater request.

    assert_equals: Number of sent beacons does not match expected count: expected 1 but got 0
```