Add custom source sha

[Kras4ooo]

Why I did this PR

I hit the issue when I created PR and when I use:

      - name: Github checkout
        uses: actions/checkout@v2
        with:
          ref: ${{ github.head_ref }}
          fetch-depth: 0

When we use github.head_ref we checkout the current branch. But after that the script gets github.sha but the value of sha is not equal to the PR value, so we have difference between the branch sha and the github.sha. I receive similar error:

  fatal: bad object 75e655dddc4f3eb8c0748b95bdd1a44f3a758b0f
  fatal: bad object 75e655dddc4f3eb8c0748b95bdd1a44f3a758b0f
  fatal: bad object 75e655dddc4f3eb8c0748b95bdd1a44f3a758b0f
  fatal: bad object 75e655dddc4f3eb8c0748b95bdd1a44f3a758b0f
  fatal: bad object 75e655dddc4f3eb8c0748b95bdd1a44f3a758b0f
  fatal: bad object 75e655dddc4f3eb8c0748b95bdd1a44f3a758b0f
  fatal: bad object 75e655dddc4f3eb8c0748b95bdd1a44f3a758b0f
  fatal: bad object 75e655dddc4f3eb8c0748b95bdd1a44f3a758b0f
  fatal: bad object 75e655dddc4f3eb8c0748b95bdd1a44f3a758b0f

With this PR we can pass the source sha and now I can pass the correct sha for the source branch and all works well.

Why I use: export GITHUB_SHA=${{ inputs.sha != '' && inputs.sha || github.sha }} vs GITHUB_SHA=${{ inputs.sha != '' && inputs.sha || github.sha }} in env section: When we use env section we pass variable but after that the Github action override GITHUB_SHA and in order to avoid this I just add export right before entrypoint execution.

[jackton1]

@Kras4ooo Thanks for implementing this fix added some updates that would be required.

[jackton1]

@all-contributors add @Kras4ooo for code and documentation

[allcontributors]

@jackton1

I've put up a pull request to add @Kras4ooo! 🎉

[jackton1]

@Kras4ooo This should be available in the latest v8.5 release. Thanks