[ci] use pip and not apt to install dependencies

Author: dnicolodi

.github/workflows/default.yml

@@ -52,12 +52,7 @@ jobs:
     - uses: actions/setup-python@v5
       with:
         python-version: ${{ matrix.python-version }}
-    - name: install dependencies
-      run: |
-        sudo apt-get update
-        sudo apt-get dist-upgrade -y
-        sudo apt-get install -y python3-sphinx
-        sudo apt-get install -y python3-docutils
+    - run: python -m pip install sphinx
     - name: documentation
       run: |
         make documentation