chore(ci): use a python version closest to the one in production

[klmp200]

Avoid python version mismatch that pulls incompatible dependencies in github actions when running unittests

[stormi]

Can you specify in the commit message what you designate as "CI"? This can be several different things: github actions, RPM %check, xcp-ng-tests runs...

[Wescoeur]

More explicit + correction regarding the used version:

This version is the closest available to the one currently used in production (3.6).

[Wescoeur]

Regarding the commit message, small suggestion:

chore(ci): build using python 3.8
Avoid python version mismatch that pulls incompatible dependencies in github actions when running unittests.

You can also explain why the coverage version is no longer forced. Regarding chore(ci) as discussed internally, it doesn't bother me if we can format the patches for the RPM while ignoring these commits with this prefix. If we can't manage that, we should explicitly state that it's the GitHub workflow. Otherwise, if it's ok I don't think there can be any misunderstanding about the term "CI."