UnitTests: Update HlslTestUtils.h include path in LongVectors.cpp (microsoft#7923)

Full explicit path not needed and breaks compatibility with Direct3D
VPack.

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Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: billkris-ms

tools/clang/unittests/HLSLExec/LongVectors.cpp

@@ -9,7 +9,8 @@
 
 #include "ShaderOpTest.h"
 #include "dxc/Support/Global.h"
-#include "dxc/Test/HlslTestUtils.h"
+
+#include "HlslTestUtils.h"
 
 #include "HlslExecTestUtils.h"