The image is for running php-cs-fixer, php-cs-fixer is installed in /app/ in case you need to customize the install before usage.
php-cs-fixer:
  stage: linting
  image: registry.gitlab.com/pipeline-components/php-cs-fixer:latest
  script:
    - php-cs-fixer fix ./ --rules=@PSR12  --verbose --show-progress=dots
  rules:
    - exists:
        - setup.py