Reduce matrix versions of python

Author: sgillies

.github/workflows/tests.yaml

@@ -16,7 +16,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["2.7", "3.7", "3.8", "3.9"]
+        python-version: ["2.7", "3.6", "3.7"]
 
     steps:
       - uses: "actions/checkout@v2"