STACKED PULL REQUESTS ARE NOW IN PUBLIC PREVIEW

Summary from the TLDR newsletter

GitHub Stacked Pull Requests break large changes into small, reviewable pull requests that each represent focused layers of the change. They allow developers to independently review and check each pull request, then merge everything together in one click. Stacked pull requests provide short, narrowly scoped pull requests, allowing developers to introduce smaller individual changes while shipping larger features. The feature is built into GitHub, so existing reviews, checks, and merge requirements all work out-of-the-box.