GitLab backups sometimes fail with file changed as we read it
GitLab backups sometimes fail if some files change while it's streaming.
The documented way to guard against exactly these kinds of issues is to use STRATEGY=copy as per https://docs.gitlab.com/ee/raketasks/backup_restore.html#backup-strategy-option. It does take 1x more disk space as there'll be a copy made before tarring stuff up but that's well worth it if it means we'll get more reliable backups.