{image,flatpak}-builder: Pin to older version of debos

The changes recently landed in the main debos branch no longer work with the old wip/uml branch of fakemachine. So until the changes are packaged in Apertis, pin to an older version of debos which has been verified to work with the wip/uml branch of fakemachine.

Signed-off-by: Christopher Obbard chris.obbard@collabora.com