added Python 3.11 testing

Author: wolph

.github/workflows/main.yml

@@ -11,7 +11,7 @@ jobs:
     timeout-minutes: 2
     strategy:
       matrix:
-        python-version: ['3.7', '3.8', '3.9', '3.10', '3.11']
+        python-version: ['3.7', '3.8', '3.9', '3.10', '3.11-dev']
 
     steps:
       - uses: actions/checkout@v2