Integrations test not testing python2

[Robin-Van-de-Merghel]

We test pylint on python2, but do not run the program on python2.

Currently, devel and main branches doesn't work because of a python2 behaviour, see #253
We would have seen it with a mamba environment for the tests.

To reproduce on python2 as well as python3 (locally), I've setup this tool.
Supports both python2 and python3, local, and remote gits.

We should improve workflows to use mamba or equiv.

[fstagni]

Ideally we would like to have the integration tests also on python2, but given that the impact of python2 is right now very small, and that one day we'll remove its support (I raised the point 1 year ago and we decided to wait a while longer), I think this would not be 100% necessary.