Merge branch '2023-08-26-bootstd-chromeos-impreovements-and-move-to-gcc-13.2' into next

First, update CI to using gcc-13.2 from 13.1, and rebuild the CI
containers.  This is needed because the second part adds utilities for
tests and provides, to quote the author:

This updates the ChromiumOS bootmeth to detect multiple kernel
partitions on a disk.

It also includes minor code improvements to the partition drivers,
including accessors for the optional fields.

This series also includes some other related tweaks in testing.