Run tests in our own testing image and for all supported python versions

.gitlab-ci.yml

@@ -10,7 +10,10 @@ lint:
 
 test:
   stage: test
-  image: python:3.10-alpine
+  parallel:
+    matrix:
+      - PY_VER: ["3.7", "3.8", "3.9", "3.10"]
+  image: $CI_REGISTRY/funkwhale/backend-test-docker:$PY_VER
   before_script: 
     - pip install poetry
     - poetry install