gitLab rules:

https://docs.gitlab.com/ee/ci/yaml/#rules

myjob:
   rules:
       - if: $CI_MERGE_REQUEST_ID
         when: always
       - when: never
   script:
       - echo "Test"

See also

• GitLab CI, variables, templates, executors, .gitlab-ci.yml, .gitlab/, Credential helpers, notifications, pipeline editor, Keyword reference, Changelog, ContainersNotReady, GitLab environments