Commits might be created by multiple authors. [GitHub supports `Co-authored-by:` for this](https://docs.github.com/en/pull-requests/committing-changes-to-your-project/creating-and-editing-commits/creating-a-commit-with-multiple-authors).

[zkoppert]

Commits might be created by multiple authors. GitHub supports Co-authored-by: for this.

The action should also report users with Co-authored-by.

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Sometimes, one can get the user information by crawling the commits of the PR. I did that in https://github.com/koppor/github-contributors-list. Would be nice if this action supported this as well.

Originally posted by @koppor in #371