bpo-39572: Address typo in CHANGELOG. (GH-24999)

(cherry picked from commit 6afb0a8)

Co-authored-by: Simon Charette <[email protected]>

Author: miss-islington

Misc/NEWS.d/3.9.0a4.rst

@@ -640,7 +640,7 @@ Adapted from a patch by Ethan Furman.
 .. nonce: CCtzy1
 .. section: Documentation
 
-Updated documentation of ``total`` flag of TypeDict.
+Updated documentation of ``total`` flag of ``TypedDict``.
 
 ..