This updates the python base images to default to trixie and python3.12
if running the builds without arguments. This isn't strictly necessary
since all of our automated builds supply these arguments. But it updates
the images for an eventual bookworm removal and rebuilds the images
which we want to do periodically anyway.
Change-Id: Ib83714ebb04b1ea6115322e305224664d6f6a78c
0b64f734bc