bpo-24650: Use full term "generator function" in yield expressions docs (GH-24663)

(cherry picked from commit 273cb8e)

Co-authored-by: Jacob Walls <jacobtylerwalls@gmail.com>

Author: miss-islington

Doc/reference/expressions.rst

@@ -422,9 +422,9 @@ Yield expressions
 The yield expression is used when defining a :term:`generator` function
 or an :term:`asynchronous generator` function and
 thus can only be used in the body of a function definition.  Using a yield
-expression in a function's body causes that function to be a generator,
+expression in a function's body causes that function to be a generator function,
 and using it in an :keyword:`async def` function's body causes that
-coroutine function to be an asynchronous generator. For example::
+coroutine function to be an asynchronous generator function. For example::
 
     def gen():  # defines a generator function
         yield 123