[SYCL][E2E] Fix a leak in test (#17444)

Fix a leak in test.

Author: yingcong-wu

sycl/test-e2e/DeprecatedFeatures/subbuffer_interop.cpp

@@ -331,6 +331,8 @@ int main() {
       std::cout << "On host: offset = " << host_acc[0] << std::endl;
       assert(host_acc[0] == 256 * 3 && "Invalid subbuffer origin");
     }
+
+    delete subbuf_copy;
   }
 
   return Failed;