Update to bookworm
Update from Debian bullseye to Debian bookworm, which has been released 2023-06-10. For health checking this release is interesting, since it should gracefully handle network booting on boards with slow network driver probe setups. For details see: https://bugs.debian.org/911727
Note, that this breaks users referencing the bullseye image. They also need to update from "bullseye" to "bookworm". E.g.: