DEBUG variable being set breaks artifacts upload
As described in gitlab-runner#3068 (closed), having a DEBUG
variable set apparently breaks artifacts upload. This issue has been open for a while and is unlikely to be fixed soon, and users are already complaining about this not at least being documented. I think it should be in the troubleshooting section here https://docs.gitlab.com/ee/ci/pipelines/job_artifacts.html#troubleshooting-job-artifacts and possibly also mentioned somewhere in https://docs.gitlab.com/ee/ci/variables/.