Update testing-cron.yml

Author: yzhao062

.github/workflows/testing-cron.yml

@@ -16,7 +16,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, windows-latest]
-        python-version: [3.6, 3.9]
+        python-version: [3.8, 3.9]
 
     steps:
     - uses: actions/checkout@v2