setup.py: Bump required Python to >= 3.6
Prepare comming changes that will require Python >= 3.6. It's time to upgrade now before any such change is merged.
GitLab Maintenance scheduled for Thursday, 18th December 2025, from 7:00 AM to 10:00 AM BST. GitLab will be in read-only mode and experience short periods of complete downtime (up to 20 minutes) during this window.
Prepare comming changes that will require Python >= 3.6. It's time to upgrade now before any such change is merged.