gh-151925: Fix minor issues in clarification introduced by gh-152463 (GH-155480)

Author: StanFromIreland

Doc/library/ast.rst

@@ -806,8 +806,11 @@ Comprehensions
    List and set comprehensions, generator expressions, and dictionary
    comprehensions. ``elt`` (or ``key`` and ``value``) is a single node
    representing the part that will be evaluated for each item.
+
    For dictionary comprehensions using unpacking, for example
-   ``{**item for item in items}``, ``value`` is ``None``,
+   ``{**item for item in items}``, the expression to be expanded goes in
+   ``key`` and ``value`` is ``None``.
+
    ``generators`` is a list of :class:`comprehension` nodes.
 
    .. doctest::