gh-106168: Update PyList_SET_ITEM() What's New doc (#111618)

Author: vstinner

Doc/whatsnew/3.13.rst

@@ -1040,7 +1040,8 @@ New Features
 * If Python is built in :ref:`debug mode <debug-build>` or :option:`with
   assertions <--with-assertions>`, :c:func:`PyTuple_SET_ITEM` and
   :c:func:`PyList_SET_ITEM` now check the index argument with an assertion.
-  If the assertion fails, make sure that the size is set before.
+  If the assertion fails in :c:func:`PyTuple_SET_ITEM`, make sure that the
+  tuple size is set before.
   (Contributed by Victor Stinner in :gh:`106168`.)
 
 * Add :c:func:`PyModule_Add` function: similar to