Feature Request: Push only the tag, not branch #153

Hi,

I'm trying to utilize this action as the last step in my release workflow.
As part of that workflow I need to push only the tag, as I have no need for a separate branch, but also I would like not to have tags on the branch I'm making it, as this branch is a "skeleton one" i.e. requires preparation before tagging, thus tags on it don't look good.

I'm reading the start.sh code and it seems there is no way to push just the tag I've just created, without pushing the branch.

https://github.com/ad-m/github-push-action/blob/master/start.sh#L52
HEAD:$INPUT_BRANCH is a branch notation, thus even if I input branch as my tag I will actually push both my tag and a branch with the same name as my tag.