[llvm] [GlobalISel] Reject scalar sources in vector truncate combine (PR #228121)

[Matt Arsenault via llvm-commits]

================
@@ -0,0 +1,45 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 6
+# RUN: llc -mtriple=amdgpu9.00-amd-amdhsa -run-pass=amdgpu-prelegalizer-combiner -verify-machineinstrs -o - %s | FileCheck %s
----------------
arsenm wrote:

```suggestion
# RUN: llc -mtriple=amdgpu9.00-amd-amdhsa -run-pass=amdgpu-prelegalizer-combiner -o - %s | FileCheck %s
```

Is it possible to merge this into an existing test file for this combine 

https://github.com/llvm/llvm-project/pull/228121