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

<img width="1494" height="1038" alt="Image" src="https://github.com/user-attachments/assets/17441f16-ff13-4c51-b2d1-7d8d1c4eea43" />