[SYCL] Fix unused_function error in post-commit (#16521)

Failure:
https://github.com/intel/llvm/actions/runs/12601531257/job/35122811530#step:12:83

Author: uditagarwal97

sycl/source/detail/os_util.cpp

@@ -59,7 +59,7 @@ inline namespace _V1 {
 namespace detail {
 
 #if defined(__INTEL_PREVIEW_BREAKING_CHANGES)
-static std::string getDirName(const char *Path)
+[[maybe_unused]] static std::string getDirName(const char *Path)
 #else
 std::string OSUtil::getDirName(const char *Path)
 #endif