Run CI tests with more Python versions (pals-project#19)

I think we would need at least this if we state that we support these
versions in pals-project#18.

Useful documentation at
https://docs.github.com/en/actions/tutorials/build-and-test-code/python.

Author: EZoni

.github/workflows/unit_tests.yml

@@ -14,12 +14,15 @@ jobs:
   unit_tests:
     name: unit tests
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.9", "3.10", "3.11", "3.12", "3.13"]
     steps:
       - uses: actions/checkout@v4
       - name: Set up Python
         uses: actions/setup-python@v5
         with:
-          python-version: "3.13"
+          python-version: ${{ matrix.python-version }}
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
@@ -30,12 +33,15 @@ jobs:
   examples:
     name: examples
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.9", "3.10", "3.11", "3.12", "3.13"]
     steps:
       - uses: actions/checkout@v4
       - name: Set up Python
         uses: actions/setup-python@v5
         with:
-          python-version: "3.13"
+          python-version: ${{ matrix.python-version }}
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip