No ..todo directive output generated #906

Describe the bug

If you look at the kitchen sink for sphinx-book-theme, there is a .. todo:: admonition directive that generates no output:

It simply gets rendered as:

By contrast, the the pydata kitchen sink looks like:

All other pydata admonitions appear to work as expected, it's just .. todo:: that behaves differently.

There's a chance this is a design choice and not a bug, but it would be nice for users to be able to choose the pydata behaviour - this might already be trivial to do, in which case a bit of clarity in the docs could also help potentially.

Thank you so much 😄

Reproduce the bug

1. Visit the pydata kitchen sink and look at the todo directive
2. Compare this to the book theme kitchen sink and its todo directive
3. Observe that the todo directive for the book theme does not render an admonition, unlike pydata

List your environment

No response