gh-151070: Fix class referencing typo in collections.abc docs (GH-151088)

(cherry picked from commit 29a920e)

Co-authored-by: Arshal Aromal <arshalaromal19@gmail.com>

Author: arshalaromal

Doc/library/collections.abc.rst

@@ -459,7 +459,7 @@ Notes on using :class:`Set` and :class:`MutableSet` as a mixin:
    The :class:`Set` mixin provides a :meth:`!_hash` method to compute a hash value
    for the set; however, :meth:`~object.__hash__` is not defined because not all sets
    are :term:`hashable` or immutable.  To add set hashability using mixins,
-   inherit from both :meth:`Set` and :meth:`Hashable`, then define
+   inherit from both :class:`Set` and :class:`Hashable`, then define
    ``__hash__ = Set._hash``.
 
 .. seealso::