[llvm] [AMDGPU][NFC] Replace gfx940 and gfx941 with gfx942 in llvm/test (PR #125711)

[Shilei Tian via llvm-commits]

https://github.com/shiltian approved this pull request.

I didn't check every single file because it took GitHub forever to load them. It looks fine after looking into 10+ files so I'll stamp green on it.

https://github.com/llvm/llvm-project/pull/125711