Feature Request: Ability to specify commit (support workflow_run)

[Scottmitch]

To support the workflow_run use case it is necessary to specify the commit to upload annotations against.

Here is an example of an action that provides this capability: https://github.com/ScaCap/action-surefire-report and here is the relevant code https://github.com/ScaCap/action-surefire-report/blob/master/action.js#L28

const commit = core.getInput('commit');
...
const head_sha = commit || (pullRequest && pullRequest.head.sha) || github.context.sha;
...
const createCheckRequest = {
        ...github.context.repo,
        name,
        head_sha,
        status,
        conclusion,
        output: {
            title,
            summary: '',
            annotations: annotations.slice(0, 50)
        }
    };

Here is an example usage of this feature: https://github.com/apache/spark/blob/master/.github/workflows/test_report.yml#L24

I think this should be relatively straight forward to add to this action, and would impact this area of code:
https://github.com/jwgmeligmeyling/spotbugs-github-action/blob/master/src/main.ts#L59

  let sha = context.sha

  if (context.payload.pull_request) {
    sha = context.payload.pull_request.head.sha
  }