use python variations in ci

Author: arcisad

.github/workflows/ci.yml

@@ -9,9 +9,18 @@ on:
 jobs:
   run-tests:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.12", "3.9"]
     name: pixi tests
     steps:
     - uses: actions/checkout@v4
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v5
+      with:
+        python-version: ${{ matrix.python-version }}
+    - name: Display Python version
+      run: python -c "import sys; print(sys.version)"
     - name: Run tests
       uses: prefix-dev/setup-pixi@v0.8.3
       with: