Python version support policy

I think it would be useful to have an explicit Python version support policy.

Here's a few aspects I'd like to propose:

• We support all feature versions (3.x) of Python from the the beginning of the release candidate phase until they reach end-of-life.
• We attempt to support pre-releases before the RC phase too, especially while they're in beta, but there may be some mismatches.
• We drop support for old versions sometime after they reach EOL, usually not immediately but only when CI maintenance starts to become a burden.
• We aim to support all bugfix releases (3.x.y) of supported feature versions. However, to keep CI sane we don't necessarily test against all possible bugfix releases.

Aucun fichier ni test n’est nommé. Commencez par localiser la documentation du dépôt et la configuration CI qui décrivent la prise en charge des versions de Python, puis comparez-les à la politique proposée. Le travail est terminé lorsque la politique concernant les versions prises en charge est documentée clairement et correspond à la couverture CI indiquée par le projet.