update examples/cpp/CMakeLists.txt to use C++20 to support concepts. The main library already uses C++20

Author: HowardHuang1

examples/cpp/CMakeLists.txt

@@ -22,6 +22,11 @@ rapids_cuda_init_architectures(test_cuvs)
 project(test_cuvs LANGUAGES CXX CUDA)
 find_package(Threads)
 
+set(CMAKE_CXX_STANDARD 20)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_CUDA_STANDARD 20)
+set(CMAKE_CUDA_STANDARD_REQUIRED ON)
+
 # ------------- configure cuvs -----------------#
 
 rapids_cpm_init()