[3.13] gh-141004: Document PyExceptionInstance* APIs (GH-141301) (GH-141303)

gh-141004: Document `PyExceptionInstance*` APIs (GH-141301)
(cherry picked from commit b5a0c72)

Co-authored-by: Peter Bierma <zintensitydev@gmail.com>
Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>

Author: 3 people

Doc/c-api/exceptions.rst

@@ -788,6 +788,17 @@ Exception Classes
 Exception Objects
 =================
 
+.. c:function:: int PyExceptionInstance_Check(PyObject *op)
+
+   Return true if *op* is an instance of :class:`BaseException`, false
+   otherwise. This function always succeeds.
+
+
+.. c:macro:: PyExceptionInstance_Class(op)
+
+   Equivalent to :c:func:`Py_TYPE(op) <Py_TYPE>`.
+
+
 .. c:function:: PyObject* PyException_GetTraceback(PyObject *ex)
 
    Return the traceback associated with the exception as a new reference, as