Describe the issue linked to the documentation

The link to the sphinx versions for doc build at the end of Building the documentation is again out-dated, with sphinx version unpinned in #27656.

Suggest a potential alternative/fix

Maybe use this link instead? https://github.com/search?q=repo%3Ascikit-learn%2Fscikit-learn+sphinx+path%3Abuild_tools%2Fcircle%2Fdoc_linux-64_conda.lock&type=code