Most builds of Trixie branches fail on Jenkins

I've seen mostly these 2 symptoms:

• build aborts during mksquashfs, either with an explicit Killed message in the console, or not
• build freezes for 1+ hour while doing the final mv of the build artifacts

IIRC @boyska recently maximized the amount of RAM we give to the Vagrant build box, relatively to the amount of RAM that the isoworkers have available, so I understand we can't simply bump the former anymore, right?