[3.14] pythongh-141004: Document PyType_Unwatch (pythonGH-141414) (pythonGH-141418)

pythongh-141004: Document `PyType_Unwatch` (pythonGH-141414)
(cherry picked from commit 759a048)

Co-authored-by: Peter Bierma <zintensitydev@gmail.com>

Author: miss-islington

Doc/c-api/type.rst

@@ -116,6 +116,20 @@ Type Objects
    .. versionadded:: 3.12
 
 
+.. c:function:: int PyType_Unwatch(int watcher_id, PyObject *type)
+
+   Mark *type* as not watched. This undoes a previous call to
+   :c:func:`PyType_Watch`. *type* must not be ``NULL``.
+
+   An extension should never call this function with a *watcher_id* that was
+   not returned to it by a previous call to :c:func:`PyType_AddWatcher`.
+
+   On success, this function returns ``0``. On failure, this function returns
+   ``-1`` with an exception set.
+
+   .. versionadded:: 3.12
+
+
 .. c:type:: int (*PyType_WatchCallback)(PyObject *type)
 
    Type of a type-watcher callback function.