Fix docs build (#14334)

The docs build is currently failing on `master`: see e.g.
https://github.com/python/mypy/actions/runs/3748461486/jobs/6365827914.

It looks like it was broken by the release of `attrs` 22.2.0 earlier
today. Specifically, it looks like
python-attrs/attrs@1bb2864
broke mypy's docs build.

I think this fixes things.

docs/source/additional_features.rst

@@ -177,7 +177,7 @@ Caveats/Known Issues
   will complain about not understanding the argument and the type annotation in
   :py:meth:`__init__ <object.__init__>` will be replaced by ``Any``.
 
-* :ref:`Validator decorators <attrs:examples_validators>`
+* :ref:`Validator decorators <attrs:examples-validators>`
   and `default decorators <http://www.attrs.org/en/stable/examples.html#defaults>`_
   are not type-checked against the attribute they are setting/validating.