Description
Pull request already closed. There are a number of causes for this issue, but the most common is someone closing/accepting a pull request in Github before MDOQ does.
MDOQ will create a pull request and then try to re-use that pull request for any further merges.
Troubleshooting
When this error occurs MDOQ drops its reference to the old pull request, so any future attempts will create a new pull request.
Simply restart the release process.