GITHUB_SHA different value for PR events about github-slug-action

[rlespinasse]

Thanks @MadJlzz for your contribution

[rlespinasse]

The goal of this github action is to expose slug/short version of existing environment variables.

To go with this philosophy, I think we can expose this kind of information, the same way we have done it for GITHUB_EVENT_REF_SLUG/GITHUB_EVENT_REF_SLUG_URL.

In this case, the possible solution will be to load a new environment variable GITHUB_EVENT_PULL_REQUEST_HEAD_SHA_SHORT in case of present of github.event.pull_request.head.sha.

[MadJlzz]

It's my first time developing a github action but it does not bother me trying. May I try with what you said?

[rlespinasse]

@MadJlzz 👍 Go for it