Run tests against Python 3.9 stable (#1348)

Co-authored-by: Tom Christie <tom@tomchristie.com>

Author: michael-k

.github/workflows/test-suite.yml

@@ -14,7 +14,7 @@ jobs:
 
     strategy:
       matrix:
-        python-version: ["3.6", "3.7", "3.8", "3.9.0-rc.2 - 3.9"]
+        python-version: ["3.6", "3.7", "3.8", "3.9"]
 
     steps:
       - uses: "actions/checkout@v2"