fix branch returning incorrect value for GitHub Actions

[mohsinulhaq]

Fixes #28

process.env.GITHUB_ACTIONS is set to true, which is the true check for GitHub actions environment.

For commits, I found no straightforward way to get the branch name.

[mohsinulhaq]

https://help.github.com/en/articles/virtual-environments-for-github-actions#default-environment-variables
Although it says GITHUB_HEAD_REF is set only for forked repositories. I tried with my personal repository and it was always available for pull requests.

[mohsinulhaq]

@siddharthkp can we merge this?

[kuldeepkeshwar]

@mohsinulhaq I couldn't find GITHUB_ACTIONS anywhere in docs. They might be using it for internal purpose.
whereas GITHUB_ACTION is always set to a unique id(IMO it is better to rely on GITHUB_ACTION).

[kuldeepkeshwar]

@mohsinulhaq Thanks 👍

[mohsinulhaq]

@kuldeepkeshwar can you also review this one: siddharthkp/bundlesize#349
both PRs are kinda related

[kuldeepkeshwar]

@mohsinulhaq I am sorry I don't have complete context here('bundlesize'). @Haroenv maybe the right person to complete the review.

PS still I will give it a try

[mohsinulhaq]

@kuldeepkeshwar can we have a new release with the fix? It's blocking our github actions pull request discovery.

[jsoref]

Fwiw, process.env.GITHUB_REF.split('/')[2] will almost certainly break various things.

By default, @dependabot uses / a lot in its branch names:

Dependabot generates a branch for each pull request. Each branch name includes dependabot, and the package manager and dependency that are updated. By default, these parts are separated by a / symbol, for example: dependabot/npm_and_yarn/next_js/acorn-6.4.1.

https://docs.github.com/en/code-security/supply-chain-security/keeping-your-dependencies-updated-automatically/configuration-options-for-dependency-updates#pull-request-branch-nameseparator

(And random people can use it as well, especially people in large organizations.)

I'm only mentioning this because my GitHub workflow broke when someone used / and I didn't have the right branch flags...