Add missing REQUIRES: spirv to vk.sampledtexture.struct.error.hlsl (#8170)

Test uses `-spirv` but lacks the `REQUIRES: spirv` annotation, so it
runs and fails under `-DENABLE_SPIRV_CODEGEN=OFF`.

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Author: damyanp

tools/clang/test/SemaHLSL/vk.sampledtexture.struct.error.hlsl

@@ -1,3 +1,4 @@
+// REQUIRES: spirv
 // RUN: %dxc -T ps_6_0 -E main %s -spirv -fcgl -verify
 
 struct Struct { float f; };