The bug

In the snapshot changelog of 18w44a, it says that the Programmer Art is an option on the resource pack menu, but this texture pack is not included in the snapshot 18w44a. Mojang already knows of this problem though, as
tweeted by Dinnerbone

Looks like the "programmer art" (old textures) resource pack was a bit shy and isn't showing up in this snapshot. We'll fix it in the next snapshot!