[NFC][AMDGPU] New test for untested case in SILowerI1Copies (#186127)
[This
line](https://github.com/ambergorzynski/llvm-project/blob/main/llvm/lib/Target/AMDGPU/SILowerI1Copies.cpp#L646)
is untested by the existing LLVM test suite (checked using code coverage
and by inserting an `abort`).
We propose a new test that exercises this case. The test is demonstrated
by adding an abort to show that it is the only test that fails (the
abort is removed before merging).