Rework CI so that we can also easily test Python 3.5

Author: lv-develer

.github/workflows/ci.yml

@@ -6,16 +6,15 @@ jobs:
     strategy:
       matrix:
         python-version:
+          - "3.5"  # Found on Ubuntu 16.04
           - "3.8"  # Found on Ubuntu 18.04 / 20.04
           - "3.10" # Found on Ubuntu 22.04
           - "3.12" # Found on Ubuntu 24.04
+    container:
+      image: python:${{ matrix.python-version }}
     steps:
       - name: Checkout
         uses: actions/checkout@v4
-      - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v5
-        with:
-          python-version: ${{ matrix.python-version }}
       - name: Set up Git inside test environment
         run: |
           git config --global user.name test