bpo-43677: Fix a minor error in Doc/howto/descriptor.rst (#25123)

It should be PyMethod_Type, not Py_MethodType.
diff --git a/Doc/howto/descriptor.rst b/Doc/howto/descriptor.rst
index 94aadd6..420d9b9 100644
--- a/Doc/howto/descriptor.rst
+++ b/Doc/howto/descriptor.rst
@@ -1064,7 +1064,7 @@
 .. testcode::
 
     class MethodType:
-        "Emulate Py_MethodType in Objects/classobject.c"
+        "Emulate PyMethod_Type in Objects/classobject.c"
 
         def __init__(self, func, obj):
             self.__func__ = func