bpo-44904: Fix classmethod property bug in doctest module (GH-28838)


The doctest module raised an error if a docstring contained an example that
attempted to access a classmethod property. (Stacking '@classmethod' on top of
`@property` has been supported since Python 3.9; see
https://docs.python.org/3/howto/descriptor.htmlGH-class-methods.)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
(cherry picked from commit b1302abcc8a4be5f39b4d60a1ce28032b77655b3)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
diff --git a/Lib/doctest.py b/Lib/doctest.py
index ba898f6..b27cbdf 100644
--- a/Lib/doctest.py
+++ b/Lib/doctest.py
@@ -1034,10 +1034,8 @@ def _find(self, tests, obj, name, module, source_lines, globs, seen):
         if inspect.isclass(obj) and self._recurse:
             for valname, val in obj.__dict__.items():
                 # Special handling for staticmethod/classmethod.
-                if isinstance(val, staticmethod):
-                    val = getattr(obj, valname)
-                if isinstance(val, classmethod):
-                    val = getattr(obj, valname).__func__
+                if isinstance(val, (staticmethod, classmethod)):
+                    val = val.__func__
 
                 # Recurse to methods, properties, and nested classes.
                 if ((inspect.isroutine(val) or inspect.isclass(val) or