Note to self:

When running an older live image without persistence (e.g. sid), the unattended
upgrades package will:
1) consume network bandwidth by downloading updated packages
2) consume memory due to the overlay filesystem
3) disrupt openQA tests due to a longer startup time and a popup about packages
that can be updated

The downloaded packages will be discarded when the machine is shut down, so
overall this is a waste of resources that can be avoided.

Example: a GNOME image for Sid from 2023-09-06T08:10:14Z needs 632MB in
/run/live/overlay after booting and downloading updated packages.