[wdspec] Avoid rounding issues with request timing assertions
Depends on D224442
Timings from the bidi network events have higher precision than what current_time returns,
allow for an extra second in the time range to avoid intermittent failures for rounding issues.
Differential Revision: https://phabricator.services.mozilla.com/D224444
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1922390
gecko-commit: a82529715a000d6e73101a936370a2c96da9f0db
gecko-reviewers: webdriver-reviewers, Sasha