pythongh-102500: Fixup some docs issues following ByteString deprecation

Author: AlexWaygood

Doc/library/collections.abc.rst

@@ -14,7 +14,9 @@
 
 .. testsetup:: *
 
-   from collections.abc import *
+   import warnings
+   with warnings.catch_warnings(action='ignore', category=DeprecationWarning):
+       from collections.abc import *
    import itertools
    __name__ = '<doctest>'
 

Doc/whatsnew/3.12.rst

@@ -831,6 +831,9 @@ Pending Removal in Python 3.14
   For use in typing, prefer a union, like ``bytes | bytearray``, or :class:`collections.abc.Buffer`.
   (Contributed by Shantanu Jain in :gh:`91896`.)
 
+* :class:`typing.ByteString`, deprecated since Python 3.9, now causes an
+  :exc:`DeprecationWarning` to be emitted when it is used or accessed.
+
 * Creating immutable types (:data:`Py_TPFLAGS_IMMUTABLETYPE`) with mutable
   bases using the C API.