Bump GitHub Action to use Python 3.13 for CI.

Author: kburke

.github/workflows/python-ci.yml

@@ -19,10 +19,10 @@ jobs:
         with:
           submodules: 'recursive'
 
-      - name: Set up Python 3.9
+      - name: Set up Python 3.13
         uses: actions/setup-python@v5
         with:
-          python-version: "3.9"
+          python-version: "3.13"
 
       - name: Upgrade Pip
         run: python -m pip install --upgrade pip