Update PR workflow to include whitelisted authors (redhat-developer#2202)

Author: themr0c

.github/workflows/pr.yml

@@ -55,6 +55,7 @@ jobs:
           organization: ${{ env.GH_ORGANIZATION }}
           gh_token: ${{ steps.app-token.outputs.token }}
           author: ${{ github.event.pull_request.user.login }}
+          whitelisted_authors: '["openshift-cherrypick-robot"]'
 
   authorize:
     # The 'external' environment is configured with the rhdh-content team as required reviewers.