bpo-35027, distutils doc: Correct note on setup.py change in Python 3.7 (GH-10032)

(cherry picked from commit e80e77a4)
Co-authored-by: TilmanK <tilman.krummeck@googlemail.com>

Doc/distutils/setupscript.rst

@@ -682,9 +682,8 @@ information is sometimes used to indicate sub-releases.  These are
           )
 
 .. versionchanged:: 3.7
-   :class:`~distutils.core.setup` now raises a :exc:`TypeError` if
-   ``classifiers``, ``keywords`` and ``platforms`` fields are not specified
-   as a list.
+   :class:`~distutils.core.setup` now warns when ``classifiers``, ``keywords``
+   or ``platforms`` fields are not specified as a list or a string.
 
 .. _debug-setup-script: