Update to Python v3.12

This also includes a new documented goal of staying on the most current
stable version of Python.

This seems like a good practice, but also we need some of the more
recent typing features.

.gitlab-ci.yml

@@ -15,6 +15,7 @@ lint:
     - make lint
 
 test:
+  image: python:3.12-bullseye
   services:
     - postgres
   stage: test

.python-version

-3.10.1
+3.12.0

README.md

@@ -4,10 +4,16 @@
 
 This project requires:
 
-- Python 3.10.x
+- Python 3.12.x
 - make
 - PostgreSQL
 
+## Python Version
+
+The project uses the `stable` release of Python (aka `bugfix`).
+
+See the [Python versions chart](https://devguide.python.org/versions/) for an up to date release timeline.
+
 ## Dev setup
 
 Once you have activated your virtual environment, install dependencies using: