Restore extra tests to 3.13.

Author: mblayman

.github/workflows/tests.yml

@@ -42,7 +42,7 @@ jobs:
       - name: Setup Python
         uses: actions/setup-python@v5
         with:
-          python-version: '3.12'
+          python-version: '3.13'
 
       - name: Install tox and any other packages
         run: pip install tox