Generating release notes using Pull Request data source is not working

When I use "prs" data source in my `.grenrc.js` file, it recognizing the correct number of closed Pull Requests but does not actually pull any data from them. I get this on my release notes: `No changelog for this release.`

The same when ran with "commits" data source, works fine and lists all the commits that occured for that tag.

Am I missing something ?

Start by reproducing the release-notes generation with the `.grenrc.js` `prs` data source, then compare it with the working `commits` source. Trace how closed pull requests are identified and converted into release-note data, using the `No changelog for this release.` output as the failure condition. Done means the `prs` source lists the pull-request data for the tag.

索引モデルが issue の本文から書いたものです。