gh-138148: Fix grammatical error in the asynchronous generator iterator term (GH-138155)

(cherry picked from commit 43b113d)

Co-authored-by: Krishna Chaitanya <[email protected]>

Author: XChaitanyaX

Doc/glossary.rst

@@ -102,7 +102,7 @@ Glossary
       statements.
 
    asynchronous generator iterator
-      An object created by a :term:`asynchronous generator` function.
+      An object created by an :term:`asynchronous generator` function.
 
       This is an :term:`asynchronous iterator` which when called using the
       :meth:`~object.__anext__` method returns an awaitable object which will execute