Fix failing tests

Author: colinodell

.github/workflows/test.yml

@@ -6,7 +6,9 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    # As long as we need Python 3.6 here in the test, we can only use up to Ubuntu 20.
+    # https://github.com/actions/setup-python/issues/544
+    runs-on: ubuntu-20.04
     strategy:
       matrix:
         include: