git rev-parse --short HEAD, we end up getting the merge commit SHA instead of most recent commit SHA of the pull request.
- for push builds, or builds not triggered by a pull request, this is the name of the branch.
- for builds triggered by a pull request this is the name of the branch targeted by the pull request.
- if the current job is a pull request, the name of the branch from which the PR originated.
- if the current job is a push build, this variable is empty (