Закрепить версию Python в CI

.gitea/workflows/ci.yaml

@@ -10,6 +10,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
       - name: Run backend tests
         run: PYTHONPATH=backend python3 -m unittest discover -s backend -p 'test_*.py' -v
       - name: Run Telegram bot tests