Update github action to setup python (#22)

Add the setup python step to configure the right python version for
running the tests.

.github/workflows/pytest.yaml

@@ -21,7 +21,13 @@ jobs:
           - '3.11'
           - '3.12'
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v4
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Display Python version
+        run: python -c "import sys; print(sys.version)"
       - run: python -m pip install --upgrade pip
       - run: python -m pip install flake8 pytest
       - run: python -m pytest -v