DOC: update sphinx and numpydoc pins #30684
Description
Currently sphinx and numpydoc are pinned to old versions in the requirements file:
numpy/requirements/doc_requirements.txt
Lines 2 to 3 in 90f6cc1
Numpydoc 1.4 is from 2022 and Sphinx 7.2.6 is from 2023.
It would behoove us to update these to the current versions so our documentation build configuration doesn't hopelessly bitrot.
I tried updating these pins in #30683 but punted when the update proved nontrivial. The build does succeed, but with more than a thousand warnings: https://gist.github.com/ngoldbaum/ad5e476401a591d378df406e2bcfaada
#28694 is related too - that's using a sphinx version newer than our pin.