option "use_repository_button" does not display button to repository

[ConnorStoneAstro]

I am really liking Jupyter-book! One strange behavior is that when we set the use_repository_button: true value, the button to link to our github doesn't appear.

You can see our _config.yml file here: https://github.com/Ciela-Institute/caustics/blob/main/docs/source/_config.yml

Here you can see our website: https://caustics.readthedocs.io/en/latest/intro.html

where there are buttons (top right) to download the page, go to full screen, and switch from light/dark mode. But the GitHub button is missing.

This might be related to a few issues #1310 , #1333, https://github.com/executablebooks/sphinx-book-theme/issues/418