[3.12] gh-101578: [doc] mention that PyErr_GetRaisedException returns NULL when the error indicator is not set (GH-113369) (#113606)

gh-101578: [doc] mention that PyErr_GetRaisedException returns NULL when the error indicator is not set (GH-113369)
(cherry picked from commit 2849cbb)

Co-authored-by: Irit Katriel <1055913+iritkatriel@users.noreply.github.com>

Author: miss-islington

Doc/c-api/exceptions.rst

@@ -427,7 +427,7 @@ Querying the error indicator
 .. c:function:: PyObject *PyErr_GetRaisedException(void)
 
    Return the exception currently being raised, clearing the error indicator at
-   the same time.
+   the same time. Return ``NULL`` if the error indicator is not set.
 
    This function is used by code that needs to catch exceptions,
    or code that needs to save and restore the error indicator temporarily.