Improve grammar in Glossary. (GH-10474)


a asynchronous generator -> an asynchronous generator
(cherry picked from commit a9655b7f71b8976c369160ef362d0e706cfcd8c9)

Co-authored-by: Windson yang <wiwindson@outlook.com>
diff --git a/Doc/glossary.rst b/Doc/glossary.rst
index b8e7737..ace7e64 100644
--- a/Doc/glossary.rst
+++ b/Doc/glossary.rst
@@ -95,7 +95,7 @@
       that it contains :keyword:`yield` expressions for producing a series of
       values usable in an :keyword:`async for` loop.
 
-      Usually refers to a asynchronous generator function, but may refer to an
+      Usually refers to an asynchronous generator function, but may refer to an
       *asynchronous generator iterator* in some contexts.  In cases where the
       intended meaning isn't clear, using the full terms avoids ambiguity.
 
@@ -389,7 +389,7 @@
       An :term:`annotation` of a function parameter or return value.
 
       Function annotations are usually used for
-      :term:`type hints <type hint>`: for example this function is expected to take two
+      :term:`type hints <type hint>`: for example, this function is expected to take two
       :class:`int` arguments and is also expected to have an :class:`int`
       return value::