Add None as a valid type in SAXParseException's second argument (#9162)

Closes #9161

stdlib/xml/sax/__init__.pyi

@@ -15,7 +15,7 @@ class SAXException(Exception):
     def __getitem__(self, ix: Any) -> NoReturn: ...
 
 class SAXParseException(SAXException):
-    def __init__(self, msg: str, exception: Exception, locator: Locator) -> None: ...
+    def __init__(self, msg: str, exception: Exception | None, locator: Locator) -> None: ...
     def getColumnNumber(self) -> int: ...
     def getLineNumber(self) -> int: ...
     def getPublicId(self): ...