mpat 0.3.0

• mpat check --gitlab renders the non-OK results as a GitLab Code Quality
  report, so drift is listed in the merge request instead of only in the job
  log. location.path is resolved against the repository root rather than the
  mpat root, because GitLab reads it relative to the checkout: a run inside
  services/api reports services/api/src/patches.py, not src/patches.py.
  The root is the nearest ancestor holding .git, which --repo-root PATH
  overrides. --gitlab and --json are mutually exclusive, and the exit code
  is unchanged, so the CI job needs artifacts: when: always to upload the
  report on the run that fails.