address review: versionchanged and whatsnew entry

Author: skirpichev

Doc/c-api/complex.rst

@@ -197,3 +197,6 @@ the :ref:`Number Protocol <number>` API or use native complex types, like
    Set :c:data:`errno` to :c:macro:`!ERANGE` on overflows.
 
    .. deprecated:: 3.15
+
+   .. versionchanged:: 3.16
+      This function leave :c:data:`errno` unchanged on success.

Doc/whatsnew/3.16.rst

@@ -1018,6 +1018,10 @@ Porting to Python 3.16
   if the value cannot be marshalled.
   (Contributed by Serhiy Storchaka in :gh:`155907`.)
 
+* :c:func:`_Py_c_abs` no longer sets :c:data:`errno` to zero on success,
+  rather leave it unchanged.
+  (Contributed by Sergey B Kirpichev in :gh:`155526`.)
+
 Deprecated C APIs
 -----------------