gitlab docker executor doesn't support bash `alias`

I have a .gitlab-ci.yml with below contents

before_script:
  - type ls
  - alias ls='ls -test'
  - type ls

And I found that the second ls says ls is /usr/bin/ls rather than ls -test aliased before, this is quite useful if alias works, e.g. configure maven local repository to CI_PROJECT_DIR/repository, so it can be cached.

before_script:
  - alias mvn="mvn -Dmaven.repo.local=$CI_PROJECT_DIR/repository"