The missing dependency was added just a few hours ago to sha256-browser (Add missing util-utf8-browser dependency by danthegoodman · Pull Request #245 · aws/aws-sdk-js-crypto-helpers · GitHub) and a new npm release has been published (https://cdn.jsdelivr.net/npm/@aws-crypto/sha256-browser/package.json).
However I’m not sure if there needs to be a new npm release for @aws-sdk/client-s3, or if there’s some other way to invalidate skypack’s cache.