[test] Add Python 3.10 (#480)

Authored-by: pukkandan, xtkoba

.github/workflows/core.yml

@@ -10,7 +10,7 @@ jobs:
       matrix:
         os: [ubuntu-18.04]
         # py3.9 is in quick-test
-        python-version: [3.7, 3.8, pypy-3.6, pypy-3.7]
+        python-version: [3.7, 3.8, 3.10-dev, pypy-3.6, pypy-3.7]
         run-tests-ext: [sh]
         include:
         # atleast one of the tests must be in windows