Add Python 3.10 to test matrix

Author: sdispater

.github/workflows/tests.yml

@@ -34,7 +34,7 @@ jobs:
     strategy:
       matrix:
         os: [Ubuntu, MacOS, Windows]
-        python-version: [3.7, 3.8, 3.9]
+        python-version: [3.7, 3.8, 3.9, "3.10"]
     steps:
       - uses: actions/checkout@v2