pythonGH-90915: Document that SystemExit doesn't trigger sys.exceptho…

…ok (python#31357)

Co-authored-by: Kumar Aditya <59607654+kumaraditya303@users.noreply.github.com>
Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>

Doc/library/sys.rst

@@ -378,7 +378,7 @@ always available.
 
    This function prints out a given traceback and exception to ``sys.stderr``.
 
-   When an exception is raised and uncaught, the interpreter calls
+   When an exception other than :exc:`SystemExit` is raised and uncaught, the interpreter calls
    ``sys.excepthook`` with three arguments, the exception class, exception
    instance, and a traceback object.  In an interactive session this happens just
    before control is returned to the prompt; in a Python program this happens just