bpo-44353: Correct docstring for `NewType` (GH-29785)


The docstring for `typing.NewType` is no longer strictly accurate, now that `NewType` is a class, rather than a function
(cherry picked from commit 93c65df83cef71a4bc77d71afecdec8744c4f73a)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
diff --git a/Lib/typing.py b/Lib/typing.py
index 21caabb..b743d40 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -2427,7 +2427,7 @@ class NewType:
     """NewType creates simple unique types with almost zero
     runtime overhead. NewType(name, tp) is considered a subtype of tp
     by static type checkers. At runtime, NewType(name, tp) returns
-    a dummy function that simply returns its argument. Usage::
+    a dummy callable that simply returns its argument. Usage::
 
         UserId = NewType('UserId', int)