actions: skip set up python step

Pip is hopefully installed by default on ubuntu

.github/workflows/doxygen.yaml

@@ -17,11 +17,6 @@ jobs:
         uses: actions/checkout@v4
       - name: Configure pages
         uses: actions/configure-pages@v3
-      - name: Add python
-        uses: actions/setup-python@v5
-        with:
-          python-version: '3.9'
-          cache: 'pip' # caching pip dependencies
       - name: Install the doxyqml filter
         run: pip install doxyqml
       - name: Doxygen