only external_pull_requests with changes is not working

Summary

Using the following will not work as expected.

only_gitlab_yml_epr:
  stage: test
  script: env
  only:
    refs:
      - external_pull_requests
    changes:
      - .gitlab-ci.yml

Editing the README will still trigger the above job even though the changes should only apply to gitlab-ci.yml

Steps to reproduce

1. Copy the job above into GitHub.
2. Import the project through Run CI/CD pipelines for external repositories
3. Update the readme in a Pull Request.

Example Project

• GitHub: https://github.com/Eagllus/gitlab-ci-test
• GitLab: http://rz.gitlab.support/pipeline_tests/gitlab-ci-test

What is the current bug behavior?

All the jobs are running.

What is the expected correct behavior?

Only the specific jobs should run.

Related customer ticket: https://gitlab.zendesk.com/agent/tickets/147083 (Internal only)