CI: fixing missing python versions

Author: rpartzsch

.github/workflows/tests.yml

@@ -8,12 +8,12 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
-      python-version: ["3.11", "3.12", "3.13"]
+      matrix:
+        python-version: ["3.11", "3.12", "3.13"]
     steps:
     # Check out repo
     - uses: actions/checkout@v4
-    - name: Setup python
-      uses: actions/setup-python@v5
+    - uses: actions/setup-python@v5
       with:
         python-version: ${{ matrix.python-version }}