Bug#943611: cegui-mk2 fails to package extensions for python 3.8

[Matthias Klose]

Package: src:cegui-mk2
Version: 0.8.7-3
Severity: important
Tags: sid bullseye patch
User: debian-python at lists.debian.org
Usertags: python3.8

when built with multiple Python3 versions, the package ends up as

Package: python3-libcegui-mk2-0.8.7
Depends: libboost-python1.67.0, libc6 (>= 2.14), libcegui-mk2-0.8.7, libgcc1 (>= 
1:3.0), libpython3.8 (>= 3.8.0~a1), libstdc++6 (>= 5.2), python3 (<< 3.8), 
python3 (>= 3.7~)

and only the 3.7 extensions in the package, despite the dependency on libpython3.8.

That should either be properly fixed, or you build for the default Python3 
version only, b-d on python3-dev instead of python3-all-dev.

Example build log from
https://launchpad.net/ubuntu/+source/cegui-mk2/0.8.7-3/+build/17964933