Read step.yml from private repository (bitrise.io workflow editor)

for my case, because of the reported issue of Git Clone step, where if you merge request from a private repository in GitLab the step fails.

related issues:

  1. Git-clone fails when PR is sent from private fork (Github)
  2. Gitlab merge request failure on git-clone step (if PR is sent from a private fork)
  3. Gitlab merge request issue on git-clone step