[3.13] gh-156970: Set Mock.return_value's docstring (GH-156971) (#156981)

(cherry picked from commit e620377)

Co-authored-by: Ivy Xu <fakeshadow1337@gmail.com>
Co-authored-by: Stan Ulbrych <stan@python.org>

Author: 3 people

Lib/unittest/mock.py

@@ -590,7 +590,7 @@ def __set_return_value(self, value):
 
     __return_value_doc = "The value to be returned when the mock is called."
     return_value = property(__get_return_value, __set_return_value,
-                            __return_value_doc)
+                            doc=__return_value_doc)
 
 
     @property

Misc/NEWS.d/next/Library/2026-09-05-15-27-11.gh-issue-156970.DxlgbB.rst

@@ -0,0 +1 @@
+Set the docstring of :attr:`unittest.mock.Mock.return_value`.