Use prebuilt Docker image for Gitea workflows

.gitea/workflows/test.yml

@@ -10,18 +10,14 @@ on:
 jobs:
   test:
     runs-on: ubuntu-latest
+    container:
+      image: daily-blackout-check-runner:latest
+    env:
+      PYTHONPATH: src
     steps:
       - name: Check out repository
         uses: https://gitea.com/actions/checkout@v4
 
-      - name: Set up Python
-        uses: https://gitea.com/actions/setup-python@v5
-        with:
-          python-version: "3.13"
-
-      - name: Install project
-        run: python -m pip install -e '.[test]'
-
       - name: Lint
         run: ruff check .