Add pre-release support to publish workflow

[matthewfeickert]

Creating the GitHub pre-release v0.7.0rc1 should have triggered the publish to PyPI workflow, but it didn't. I don't think that there is a pre_release github.event_name

pyhf/.github/workflows/publish-package.yml

Lines 104 to 105 in acde7f4

	- name: Publish distribution 📦 to PyPI
	if: github.event_name == 'release' && github.event.action == 'published' && github.repository == 'scikit-hep/pyhf'

so we'll need to figure out how release candidate pre-releases can get integrated in.

[matthewfeickert]

So seems that I need to learn the github.event API better as there is apparently a github.event.release.prerelease. So I now don't know how github.event_name and github.event.release's attributes differ.

edit
Under https://docs.github.com/en/rest/releases/releases#create-a-release there is

prerelease boolean
true to identify the release as a prerelease. false to identify the release as a full release.
Default: false

Thought this seems to imply that a prerelease is not a published event.action(?).

[matthewfeickert]

I think https://github.com/orgs/community/discussions/26281#discussioncomment-3251177 is how to do this.