Move minimum supported Python to 3.10

Author: stefanv

.github/workflows/tests.yaml

@@ -36,7 +36,7 @@ jobs:
         include:
           # Only test oldest supported and latest python version to reduce
           # GitHub API calls, as they can get rate limited
-          - python-version: 3.9
+          - python-version: 3.10
           - python-version: 3.x
 
     steps: