Bug 1691109 [wpt PR 27513] - Increase timeout duration for wpt/fetch/api/basic/keepalive.html, a=testonly

Automatic update from web-platform-tests
Increase timeout duration for wpt/fetch/api/basic/keepalive.html

[1] shows that the tests in the file is flaky. flake portal's current
flakiness score is about 1600. Increase the timeout duration to make it
less flaky.

1: https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=blink_web_tests&tests=wpt%2Ffetch%2Fapi%2Fbasic%2Fkeepalive.html

Bug: None
Change-Id: I9535aa43a1464adcb52fe7dd7ef19da99ea69924
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2678821
Auto-Submit: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Dominic Farolino <dom@chromium.org>
Reviewed-by: Dominic Farolino <dom@chromium.org>
Cr-Commit-Position: refs/heads/master@{#852470}

--

wpt-commits: 5c46bbe8d09ff44e4f9186f137f28a3c5574a483
wpt-pr: 27513

testing/web-platform/tests/fetch/api/basic/keepalive.html

@@ -42,7 +42,7 @@ async function queryToken(token) {
 // an async_test.
 function checkToken(testName, token) {
   async_test((test) => {
-    new Promise((resolve) => test.step_timeout(resolve, 1000)).then(() => {
+    new Promise((resolve) => test.step_timeout(resolve, 3000)).then(() => {
       return queryToken(token);
     }).then((result) => {
       assert_equals(result, 'on');