Support passing in SHA of commit to associate check

[flcdrg]

If you're separating out workflows like in https://docs.github.com/en/code-security/supply-chain-security/keeping-your-dependencies-updated-automatically/automating-dependabot-with-github-actions#handling-push-events then you might want to run this action from a workflow triggered by the workflow_run event.

In that case the current logic doesn't pick up the correct commit SHA. In this situation it would be great to have a property that can be set to the SHA..

eg.

        with:
          report_name: Unit Tests
          report_title: Unit Tests
          github_token: ${{ secrets.GITHUB_TOKEN }}
          test_results_path: ./TestResults.trx
          sha: ${{ github.event.workflow_run.head_sha }}