After spending hours and hours on the NASA website researching an answer to your question, I finally have come to a date. Never.
It’s not the surface of the sun you have to worry about, but the corona, which I managed to photograph during the eclipse of 2017 in Missouri. Not the best shot but here it is. The corona is even hotter than the sun. We’re not exactly sure why that is, but you’ve got to get through that before you get to the surface! In this picture, taken with a cheap cannon digital camera with a cheap telephoto lens, the moon is blocking the sun. Slight pink marks at the edge are solar flares that were taking place during the eclipse. The white stuff is called the corona. Essentially, this is the sun’s atmosphere. You’re going to burn up there before you reach the burning surface!