Favour GITHUB_HEAD_REF for branch name when present (pull requests)

[BDQ]

For actions triggered on pull_request, the GITHUB_REF does not contain the branch name it generally looks something like 0371/merge - resulting in workflow API calls returning no run data.

This change will use GITHUB_HEAD_REF as the first preference for the branch name when it is present (it is only present in pull request actions). Relevant snippet from the Actions docs

[BDQ]

I've run a few test actions to show the before/after states - and confirm no regression.

pull_request trigger - current v1 release - Not waiting
(BAD): https://github.com/BDQ/test-actions/runs/804677535?check_suite_focus=true
(First run, which should have blocked it): https://github.com/BDQ/test-actions/runs/804677034?check_suite_focus=true

pull_request trigger - with PR changes - waiting correctly
(GOOD): https://github.com/BDQ/test-actions/runs/804668836?check_suite_focus=true

Non pull_request trigger - with PR changes - still works
(STILL GOOD): https://github.com/BDQ/test-actions/runs/804637766?check_suite_focus=true

[softprops]

Nice catch. I rarely use pull_request events and just use pushes to pull requested branches so I missed this

[softprops]

updated the latest tag with this change