ci(sphinx): use python 3.12 for sphinx build

.github/workflows/sphinx.yml

@@ -9,10 +9,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
 
-      - name: Set up Python 3.9
+      - name: Set up Python 3.12
         uses: actions/setup-python@v1
         with:
-          python-version: 3.9
+          python-version: "3.12"
 
       - name: Install apt dependencies
         run: |