another try. list of strings for toplevel.

[skip travis]

Author: rouilj

.github/workflows/ci-test.yml

@@ -61,7 +61,7 @@ jobs:
         os: [ubuntu-latest, ubuntu-20.04]
 
         # if the ones above fail. fail the build
-        experimental: false
+        experimental: [ "false" ]
 
         include:
             # example: if 3.12 fails the jobs still succeeds