CI config `always` option aside `only`/`except`

Problem to solve

We want to run jobs in MRs only when related files changed and always for master branch.

Further details

Security and stability reasons.

Proposal

always option aside only/except options in CI config.

What does success look like, and how can we measure that?

rubocop:
  image: ruby:2.5.3
  stage: lint
  script:
    - bundle exec rubocop
  only:
    changes:
      - Gemfile.lock
      - .rubocop.yml
      - '**/*.rb'
  always:
    branches:
      - master

Links / references