.gitlab-setup should use an env variable to specify the repo URL for gitlab-test

Everyone can contribute. Help move this issue forward while earning points, leveling up and collecting rewards.

• Close this issue

Similarly to what we've done in SeedHelper with GITLAB_GIT_TEST_REPO_URL, the repo URL for gitlab-test should be overridable via CI secret variables in the .gitlab-setup CI jobs.

This will prevent pipelines from failing on dev when GitLab.com is down (e.g. https://dev.gitlab.org/gitlab/gitlabhq/builds/1107732).

Related to gitlab-ce#32492.