Try testing on oldest supported version

Author: cphyc

.github/workflows/pytest.yml

@@ -15,7 +15,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.11", "3.13"]
+        python-version: ["3.9", "3.13"]
 
     steps:
     - uses: actions/checkout@v4