Describe the bug

My cmd:
/usr/local/bin/sphinx-build -b man -t man -d /root/bu/ceph/build/doc/doctrees -c /root/bu/ceph/man /root/bu/ceph/doc/man /root/bu/ceph/build/doc/man

Error Message:
Running Sphinx v1.7.6
loading pickled environment... not yet created
building [mo]: targets for 0 po files that are out of date
building [man]: all manpages
updating environment: 46 added, 0 changed, 0 removed
reading sources... [ 2%] 8/ceph
reading sources... [ 4%] 8/ceph-authtool
reading sources... [ 6%] 8/ceph-bluestore-tool

Exception occurred:
File "/usr/local/Python-3.6.15/lib/python3.6/site-packages/Sphinx-1.7.6.dev20211011-py3.6.egg/sphinx/util/nodes.py", line 57, in apply_source_workaround
for classifier in reversed(node.parent.traverse(nodes.classifier)):
TypeError: 'generator' object is not reversible
The full traceback has been saved in /tmp/sphinx-err-jpnnyy28.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at https://github.com/sphinx-doc/sphinx/issues. Thanks!

How to Reproduce

I download the sphinx from https://github.com/sphinx-doc/sphinx.
And build it with "python3 setup.py install".

Expected behavior

No response

Your project

https://github.com/ceph/ceph

Screenshots

No response

OS

CentOS Linux release 7.9.2009 (Core)

Python version

Python 3.6.15

Sphinx version

sphinx-1.7.6.tar.gz

Sphinx extensions

No response

Extra tools

No response

Additional context

No response