[3.13] gh-137043: mention PyList_GET_ITEM as unsafe borrowed API in free-threading docs (GH-137042) (#137046)

gh-137043: mention `PyList_GET_ITEM` as unsafe borrowed API in free-threading docs (GH-137042)
(cherry picked from commit 38b936c)

Co-authored-by: Guido Imperiale <crusaderky@gmail.com>

Author: miss-islington

Doc/howto/free-threading-extensions.rst

@@ -159,6 +159,8 @@ that return :term:`strong references <strong reference>`.
 +===================================+===================================+
 | :c:func:`PyList_GetItem`          | :c:func:`PyList_GetItemRef`       |
 +-----------------------------------+-----------------------------------+
+| :c:func:`PyList_GET_ITEM`         | :c:func:`PyList_GetItemRef`       |
++-----------------------------------+-----------------------------------+
 | :c:func:`PyDict_GetItem`          | :c:func:`PyDict_GetItemRef`       |
 +-----------------------------------+-----------------------------------+
 | :c:func:`PyDict_GetItemWithError` | :c:func:`PyDict_GetItemRef`       |