Use container for CI workflow

.gitea/workflows/ci.yml

@@ -5,22 +5,16 @@ on: [push, pull_request]
 jobs:
   test:
     runs-on: ubuntu-latest
+    container: python:3.11-slim
     steps:
-      - name: Checkout
-        run: |
-          echo "Gitea Actions automatically checks out code"
-          ls -la
-
-      - name: Set up Python
-        run: |
-          python -m pip install --upgrade pip
-          python --version
+      - name: Checkout code
+        uses: actions/checkout@v4
 
       - name: Install dependencies
         run: |
+          pip install --upgrade pip
           pip install -r requirements.txt
           pip install pytest
 
       - name: Run tests
-        run: |
-          pytest tests/ -v
+        run: pytest tests/ -v