ci: Run tests against python 3.12

Part-of: <https://dev.funkwhale.audio/funkwhale/funkwhale/-/merge_requests/2660>

.gitlab-ci.yml

@@ -231,7 +231,7 @@ test_api:
   image: $CI_REGISTRY/funkwhale/ci/python-funkwhale-api:$PYTHON_VERSION
   parallel:
     matrix:
-      - PYTHON_VERSION: ["3.8", "3.9", "3.10", "3.11"]
+      - PYTHON_VERSION: ["3.8", "3.9", "3.10", "3.11", "3.12"]
   services:
     - name: postgres:15-alpine
       command: