test: skip failing tests for osx mojave

Refs: https://github.com/nodejs/node/issues/21679
PR-URL: https://github.com/nodejs/node/pull/23550


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: George Adams <george.adams@uk.ibm.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>