Switch to `GIT_STRATEGY=fetch` for `www-gitlab-com` repo

Switch to GIT_STRATEGY=fetch for www-gitlab-com repo to reduce the repo cloning time. Currently it defaults to clone.

If fetch is specified and the job's docker instance already has the repo cloned, it can reduce the time for this step from 1:30-2:00 minutes or more down to 20 seconds.

UPDATE: In some cases, the checkout time is as little as seven seconds

NOTE: See the epic for more context on the effort to reduce repo cloning time.