This was still set to bullseye which isn't a problem for our Zuul jobs
as they always specify what version to use. However, local builds would
build bullseye by default which isn't super useful now that the vast
majority of images are built on top of bookworm. Swap things around to
avoid potential confusion.
Change-Id: If68e32a358268a423e35e44e3150115cd1da6f8c