[llvm] [NFC][AMDGPU] New test for untested case in SILowerSGPRSpills (PR #189426)

[Robert Imschweiler via llvm-commits]

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@@ -1,3 +1,4 @@
+# NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 6
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ro-i wrote:

I think this should be autogenerated by `update_mir_test_checks.py`

https://github.com/llvm/llvm-project/pull/189426