[3.12] gh-115249: Fix test_descr with -OO mode (GH-115250) (#115277)

gh-115249: Fix `test_descr` with `-OO` mode (GH-115250)
(cherry picked from commit 1f23837)

Co-authored-by: Nikita Sobolev <[email protected]>

Author: miss-islington

Lib/test/test_descr.py

@@ -1594,7 +1594,11 @@ def f(cls, arg):
 
         cm = classmethod(f)
         cm_dict = {'__annotations__': {},
-                   '__doc__': "f docstring",
+                   '__doc__': (
+                       "f docstring"
+                       if support.HAVE_DOCSTRINGS
+                       else None
+                    ),
                    '__module__': __name__,
                    '__name__': 'f',
                    '__qualname__': f.__qualname__}