Make yarn builds fault tolerant of yarnpkg.com
Recently it seems the yarn package server has hit some downtime (e.g. just now in https://dev.gitlab.org/gitlab/gitlabhq/-/jobs/2468682): https://twitter.com/jamiebuilds/status/1000198463269699584
Should we be putting a cache in front of this to avoid build failures?
Edited by Stan Hu