The Dart SDK 2.17.1 was released on 18 May 2022, and versions.json and the Dockerfile SHAs were updated in the dart-lang/dart-docker repo that same day with PR #94.
Since then there have been fresh releases of library/dart, presumably for other upstream dependencies. But it remains firmly fixed on 2.17.0.
I’d expect the update to take a day or so, but after 12 days waiting it’s looking like something is broken.