Clean changelog_unreleased

scripts/release/steps/clean-changelog.js

@@ -20,3 +20,5 @@ export default async function cleanChangelog({ repo }) {
   await runGit(["commit", "-am", "Clean changelog_unreleased"]);
   await runGit(["push", "--repo", repo]);
 }
+
+await cleanChangelog({ repo: "prettier/prettier" });