Release Operator GHA changelog is wrong

# Description
Running the Release Operator changelog creates a release with a changelog from all merged PRs since the beginning of the repo rather than the last release, requiring the changelog to be manually refined after the release is created

Start by locating the Release Operator GitHub Actions workflow that generates the changelog and inspect how it determines the previous release. Compare its output with the most recent release; done means the generated changelog includes only merged PRs since that release and no longer requires manual refinement.

Written by the indexing model from the issue text.