Drop support for Python `3.6`, `3.7`, add for `3.10`, `3.11`

[xzmeng]

Python 3.6, 3.7 have reached their end-of-life of their release cycles.
Current tests workflow will fail because actions/setup-python does not provide 3.6 on ubuntu-latest:
So I propose to update the Python versions and happy to make a PR if you think it reasonable.

[nardew]

Hi @xzmeng , thanks for pointing this out. If you can open a PR with all the changes, that would be great. Thanks!