distro/pkg/deb: depend on python3, not python3-all

This fixes build failures on Ubuntu 24.04 in LaunchPad.

For some reason, both python3.11 and python3.12 are pulled during build and 3.12 manager build fails with missing Python.h from libpython3.12-dev.

For now, explicitly depend on libpython3.12-dev on Ubuntu 24.04, but hopefully the packaging situation improves so that this isn't necessary.