Fix tests

Author: HardNorth

.github/workflows/tests.yml

@@ -19,7 +19,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       matrix:
         python-version: [ '2.7', '3.6', '3.7', '3.8', '3.9', '3.10' ]