ci: use ubuntu-latest with python container

.forgejo/workflows/test.yml

@@ -3,8 +3,13 @@ on: [push, pull_request]
 
 jobs:
   test:
-    runs-on: python
+    runs-on: ubuntu-latest
+    container:
+      image: python:3.11-slim
     steps:
+      - name: Install git
+        run: apt-get update && apt-get install -y git
+
       - uses: https://github.com/actions/checkout@v4
 
       - name: Install dependencies