Found in the files of the recently dumped TimeSplitters 4 tech demo alongside a bunch of other textual GoldenEye references (twitter link) like description files for every single level from the original game and "dam_new"
Path to the actual skybox texture file inside the pak archive is assets\ts\tex_cl_v8\goldeneye\default_sky.clt, the only file in that "goldeneye" folder so on a really surface level comb it might be the only actual visual file from the remake in this build
Spinning visualisation inspired by @skyboxsatellite
Actual ripped / converted graphic of the skybox looks like this
Might be indeed just a default sky copied from elsewhere and used as a placeholder, might even be from a third-party pack somewhere, but looks very nice nonetheless, I like the purplish mist and general vibe a lot