Docs: sphinx-notfound-page doesn't show nicer 404 page

[nineteendo]

Documentation

The sphinx not found extension introduced in #111084 doesn't seem to be installed when the documentation is published: https://docs.python.org/3/-

This is how it's meant to look: https://cpython-previews.readthedocs.io/en/3.14/-

cc @hugovk

[hugovk]

I can see the extension is installed in the venv on the docs server, for example:

./venv-3.14/lib/python3.10/site-packages/sphinx_notfound_page-1.0.4.dist-info
./venv-3.14/lib/python3.10/site-packages/sphinx_notfound_page-1.0.4.dist-info/RECORD
./venv-3.14/lib/python3.10/site-packages/sphinx_notfound_page-1.0.4.dist-info/WHEEL
./venv-3.14/lib/python3.10/site-packages/sphinx_notfound_page-1.0.4.dist-info/INSTALLER
./venv-3.14/lib/python3.10/site-packages/sphinx_notfound_page-1.0.4.dist-info/LICENSE
./venv-3.14/lib/python3.10/site-packages/sphinx_notfound_page-1.0.4.dist-info/REQUESTED
./venv-3.14/lib/python3.10/site-packages/sphinx_notfound_page-1.0.4.dist-info/METADATA
./venv-3.14/lib/python3.10/site-packages/notfound
./venv-3.14/lib/python3.10/site-packages/notfound/__pycache__
./venv-3.14/lib/python3.10/site-packages/notfound/__pycache__/__init__.cpython-310.pyc
./venv-3.14/lib/python3.10/site-packages/notfound/__pycache__/extension.cpython-310.pyc
./venv-3.14/lib/python3.10/site-packages/notfound/__pycache__/utils.cpython-310.pyc
./venv-3.14/lib/python3.10/site-packages/notfound/__init__.py
./venv-3.14/lib/python3.10/site-packages/notfound/extension.py
./venv-3.14/lib/python3.10/site-packages/notfound/utils.py

I'm not sure what's up, perhaps it's some Nginx config?

But at least it is useful on the previews, and there is a plan to host the docs on Read the Docs: https://github.com/python/docs-community/issues/5.