Environment Variable being ignored when set in `rules:changes`

Summary

When setting an environment variable as a path and using that variable in rules:changes, the variable is ignored.

Steps to reproduce

1. Create a env variable named HELM_DIR and set it to 'helm' in the UI.

2. Create a project that contains helm/test.txt

3. Add the below gitlab-ci.yml script to the project:

test0:
  script:
    - echo "This is test0 and will complete"
    - echo $CI_COMMIT_BRANCH
    - echo $CI_PROJECT_DIR

test1:
  script:
    - echo $CI_COMMIT_BRANCH
    - echo $CI_PROJECT_DIR
    - echo $HELM_DIR
    - echo "This is working"
    - ls
  rules:
    - if: $CI_COMMIT_BRANCH
      changes:
      - $HELM_DIR/**/*
      when: on_success

4. Make a change to the helm/test.txt file or any file in that folder.

The below works when explicitly setting the file path:

test0:
  script:
    - echo "This is test0 and will complete"
    - echo $CI_COMMIT_BRANCH
    - echo $CI_PROJECT_DIR

test1:
  script:
    - echo $CI_COMMIT_BRANCH
    - echo $CI_PROJECT_DIR
    - echo "This is working"
    - ls
  rules:
    - if: $CI_COMMIT_BRANCH
      changes:
      - helm/**/*
      when: on_success

Example Project

https://gitlab.com/ehenley/rules_changes (Private project)

Was able to recreate this on self-managed and on .com.

What is the current bug behavior?

When setting a path as an env variable, and using the env in rules:changes, the path is never evaluated.

What is the expected correct behavior?

The env variable should act the same as explicitly setting the path in the ci.