fix(ci): test Python 3.9 instead of 3.8

Author: MilesCranmerBot

.github/workflows/CI.yml

@@ -43,7 +43,7 @@ jobs:
             os: ubuntu-latest
             test-id: include
           - julia-version: '1'
-            python-version: '3.8'
+            python-version: '3.9'
             os: ubuntu-latest
             test-id: include