[3.13] gh-121749: Fix discrepancy in docs for PyModule_AddObjectRef (GH-121750) (GH-121752)

(cherry picked from commit 26dfb27)

Co-authored-by: Dominic H <dom@dominic.sk>

Author: miss-islington

Doc/c-api/module.rst

@@ -517,7 +517,7 @@ state:
 
    On success, return ``0``. On error, raise an exception and return ``-1``.
 
-   Return ``NULL`` if *value* is ``NULL``. It must be called with an exception
+   Return ``-1`` if *value* is ``NULL``. It must be called with an exception
    raised in this case.
 
    Example usage::

Misc/NEWS.d/next/Documentation/2024-07-14-11-48-10.gh-issue-121749.nxHoTk.rst

@@ -0,0 +1 @@
+Fix documentation for :c:func:`PyModule_AddObjectRef`.