Set backport PR reviewer equal to original PR reviewer

[korthout]

Original issue: https://github.com/zeebe-io/automation-lab/issues/39

[korthout]

This implementation never really seems to have worked as expected. The requested_reviewers often seems to be empty. However, a special api is available to retrieve this data.

const reviews = await github
        .getOctokit(token)
        .pulls.listReviews({owner, repo, pull_number: number})

See this under Run ./actions/hello-world-typescript (the last printed part) as an example of this api's returned data.