[clang] clang: Fix broken check prefix in test (PR #119821)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `arc-builder` running on `arc-worker` while building `clang` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/3/builds/9101

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
...
10.822 [32/18/28] Linking CXX executable unittests/DebugInfo/BTF/DebugInfoBTFTests
10.856 [31/18/29] Linking CXX executable unittests/DebugInfo/GSYM/DebugInfoGSYMTests
11.110 [30/18/30] Linking CXX executable unittests/DWARFLinkerParallel/DWARFLinkerParallelTests
11.549 [29/18/31] Linking CXX executable unittests/Debuginfod/DebuginfodTests
11.754 [28/18/32] Linking CXX executable unittests/DebugInfo/PDB/DebugInfoPDBTests
11.881 [27/18/33] Linking CXX executable unittests/ExecutionEngine/ExecutionEngineTests
12.185 [26/18/34] Linking CXX executable unittests/ExecutionEngine/JITLink/JITLinkTests
12.500 [25/18/35] Linking CXX executable tools/clang/unittests/Tooling/ToolingTests
12.712 [24/18/36] Linking CXX executable unittests/InterfaceStub/InterfaceStubTests
13.690 [23/18/37] Linking CXX executable unittests/FuzzMutate/FuzzMutateTests
command timed out: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=1214.442181

```

</details>

https://github.com/llvm/llvm-project/pull/119821