pytest has crashed on testing with python 3.10.0a7

[tk0miya]

Describe the bug
pytest has crashed on testing with python 3.10.0a7

refs:

• https://github.com/sphinx-doc/sphinx/runs/2316803365?check_suite_focus=true
• Assertion rewriting fails under Python 3.10.0a7+ pytest-dev/pytest#8539

[tk0miya]

As a workaround, I disable the CI with python3.10 for a while.