[llvm] [NFC][AMDGPU] Add test for unfold-masked-merge-scalar-variablemask.ll (PR #140093)

[Harrison Hao via llvm-commits]

harrisonGPU wrote:

Hi @shiltian @arsenm , could you please take a look this lit test if you have time, this PR aims for this https://github.com/llvm/llvm-project/pull/112647

https://github.com/llvm/llvm-project/pull/140093