Hmmm... this is very interesting . I looked up in Sanbi-website , and it appears their distribution do include the WESTERN parts of Gauteng :
The Cape cobra is endemic to southern Africa and is found widely in the Western and Northern Cape provinces, and into the Free State, North West Province, western parts of Gauteng, Eastern Cape, Botswana and southern Namibia. It is restricted to the western deserts and scrublands of southern Africa.
You learn something new every day