The readme has the following line:

This will create a Release, as well as a release event, which could be handled by a third party service, or by GitHub Actions for additional uses, for example the @actions/upload-release-asset GitHub Action.

I think there should be some clarification that a release event created with the default github.token (or secrets.GITHUB_TOKEN), will not trigger another workflow. The user will have to use a personal access token for this to work.