PDF build issue

[JulienPalard]

Since https://github.com/python/python-docs-ja/issues/34 and https://github.com/python/python-docs-ja/issues/31 I have issues building PDFs on docs.python.org, it can easily be reproduced using https://github.com/python/docsbuild-scripts/ as:

./build_docs.py --build-root ./build_root --www-root ./www --log-directory ./logs --group $(id -g) --skip-cache-invalidation --language ja --branch 3.9

(you can easily try other branches by changing the --branch argument)