Run CI with Python 3.11

Author: wch

.github/workflows/pytest.yaml

@@ -14,7 +14,7 @@ jobs:
     strategy:
       matrix:
         # "3.10" must be a string; otherwise it is interpreted as 3.1.
-        python-version: [3.7, 3.8, 3.9, "3.10"]
+        python-version: [3.7, 3.8, 3.9, "3.10", 3.11]
       fail-fast: false
 
     steps: