Update base Python image to 3.11

With the release of Python 3.12, scheduled for October 2nd, we should update the base Python image to 3.11.

added P3 label

assigned to @eigenwijsje

changed milestone to %1.0-alpha3 — Playful Platypus

added Doing label

closed with commit c22d6939

removed Doing label

mentioned in commit c22d6939