CI: Bump python versions to 3.8, 3.9, 3.10

Author: tony

.github/workflows/tests.yml

@@ -34,7 +34,7 @@ jobs:
         runs-on: ubuntu-latest
         strategy:
             matrix:
-                python-version: [3.6, 3.7, 3.8]
+                python-version: [3.8, 3.9, 3.10]
         steps:
             - uses: actions/checkout@v2
             - name: Set up Python ${{ matrix.python-version }}