voluptuous now requires python 3.7 to work

[remi-delmas-3000]

cbmc-viewer depends on voluptuous which recently (Nov 2023) upgraded from 0.13.1 to 0.14.0. This new version uses __future__.annotations which silently require python 3.7 to work (https://github.com/alecthomas/voluptuous/issues/490).

cbmc-viewer only lists python 3.6 as minimum required version, so we have a silent conflict on the python version.

One solution could be to impose an upper bound 0.13.1 on voluptuous, or bump the minimum python version to 3.7 for cbmc-viewer.