Run flake8 with Python 3.13

Python version 3.14 no longer works.

Author: arthurdejong

.github/workflows/test.yml

@@ -36,7 +36,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v4
         with:
-          python-version: 3.x
+          python-version: 3.13
       - name: Install dependencies
         run: python -m pip install --upgrade pip tox
       - name: Run tox ${{ matrix.tox_job }}