[3.13] gh-141004: Document Py_MakePendingCalls (GH-141137) (GH-141788)

gh-141004: Document `Py_MakePendingCalls` (GH-141137)
(cherry picked from commit ce70103)

Co-authored-by: Peter Bierma <zintensitydev@gmail.com>
Co-authored-by: Victor Stinner <vstinner@python.org>

Author: 3 people

Doc/c-api/init.rst

@@ -1964,6 +1964,25 @@ pointer and a void pointer argument.
       This function now always schedules *func* to be run in the main
       interpreter.
 
+
+.. c:function:: int Py_MakePendingCalls(void)
+
+   Execute all pending calls. This is usually executed automatically by the
+   interpreter.
+
+   This function returns ``0`` on success, and returns ``-1`` with an exception
+   set on failure.
+
+   If this is not called in the main thread of the main
+   interpreter, this function does nothing and returns ``0``.
+   The caller must hold the :term:`GIL`.
+
+   .. versionadded:: 3.1
+
+   .. versionchanged:: 3.12
+      This function only runs pending calls in the main interpreter.
+
+
 .. _profiling:
 
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