DEPR: is_bool_dtype special-casing Index[object_all_bools]

[jbrockmendel]

• closes #xxxx (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

I'm pretty sure this is a leftover kludge from before we supported bool dtype Indexes.

[mroeschke]

 sort whatsnew entries alphabetically....................................................................Failed
- hook id: sort-whatsnew-items
- duration: 0.05s
- exit code: 1
- files were modified by this hook
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diff --git a/doc/source/whatsnew/v2.1.0.rst b/doc/source/whatsnew/v2.1.0.rst
index db8e683..841419a 100644
--- a/doc/source/whatsnew/v2.1.0.rst
+++ b/doc/source/whatsnew/v2.1.0.rst
@@ -232,10 +232,10 @@ Deprecations
 - Deprecated parameter ``convert_type`` in :meth:`Series.apply` (:issue:`52140`)
 - Deprecated passing a dictionary to :meth:`.SeriesGroupBy.agg`; pass a list of aggregations instead (:issue:`50684`)
 - Deprecated the "fastpath" keyword in :class:`Categorical` constructor, use :meth:`Categorical.from_codes` instead (:issue:`20110`)
+- Deprecated the behavior of :func:`is_bool_dtype` returning ``True`` for object-dtype :class:`Index` of bool objects (:issue:`52680`)
 - Deprecated the methods :meth:`Series.bool` and :meth:`DataFrame.bool` (:issue:`51749`)
 - Deprecated unused "closed" and "normalize" keywords in the :class:`DatetimeIndex` constructor (:issue:`52628`)
 - Deprecated unused "closed" keyword in the :class:`TimedeltaIndex` constructor (:issue:`52628`)
-- Deprecated the behavior of :func:`is_bool_dtype` returning ``True`` for object-dtype :class:`Index` of bool objects (:issue:`52680`)

[jbrockmendel]

updated+green

[mroeschke]

Thanks @jbrockmendel