gh-95914: Add to what's new a credit for pep 678 author by iritkatriel · Pull Request #95955 · python/cpython

Thanks @iritkatriel — since there would be a merge conflict with #95915 otherwise, I cherry-picked your commit into that PR's branch and fixed the conflicts there, so this could be closed once that's merged (I added a close tag there, but those don't always work for PRs, unfortunately).