Given that

... the [np.testing.dec] decorators are only retained for folks using the old nose framework and will be removed as some point, nose doesn't work with recent Python without modification. Most distros no longer provide nose, but rather nose2.

@charris in #16370 (comment)

I think we should update the docs at https://numpy.org/devdocs/reference/routines.testing.html#decorators to make this clear.

We might also want to consider deprecating them fully with DeprecationWarnings