Update sphinx.yml

Fixed python version to perform GH action.

Author: ffrancesco94

.github/workflows/sphinx.yml

@@ -21,7 +21,7 @@ jobs:
       - name: Install Python
         uses: actions/setup-python@v1
         with:
-          python-version: 3.8
+          python-version: 3.11.11
       - name: Fetch all refs
         run: |
           git fetch