Describe the bug

Recently, types.Union was renamed to types.UnionType on the HEAD of 3.10 (refs: python/cpython#27342). After this change, sphinx-build has been crashed because of ImportError.

How to Reproduce

$ tox -e py310

Expected behavior

CI has passed.

Your project

N/A

Screenshots

No response

OS

Linux

Python version

HEAD of 3.10

Sphinx version

4.1.x

Sphinx extensions

No response

Extra tools

No response

Additional context

No response