DOC: Turn on nitpicky mode to catch broken ref

[pllim]

At the time of writing, it is disabled:

jwst/docs/conf.py

Line 494 in 6840699

nitpicky = False

If you enable it, you will see all broken refs reported and blocking RTD build (because it also turns warnings into exceptions) until they are fixed:

jwst/.readthedocs.yaml

Line 12 in 6840699

fail_on_warning: true

Also see: https://www.sphinx-doc.org/en/master/usage/configuration.html#options-for-the-nitpicky-mode