Update whatsnew

Author: sergey-miryanov

Doc/whatsnew/3.15.rst

@@ -315,7 +315,7 @@ Limited C API changes
 
 * If the :c:macro:`Py_TPFLAGS_MANAGED_DICT` and :c:macro:`Py_TPFLAGS_MANAGED_WEAKREF`
   flags are set then :c:macro:`Py_TPFLAGS_HAVE_GC` should be set too.
-  (Contributed by Sergey Miryanov.)
+  (Contributed by Sergey Miryanov in :gh:`134786`)
 
 
 Porting to Python 3.15