Update nvbench configuration to use C++20 standard (#1141)

Author: cliffburdick

CMakeLists.txt

@@ -456,7 +456,10 @@ if (MATX_BUILD_EXAMPLES)
 endif()
 
 if (MATX_BUILD_BENCHMARKS)
-    rapids_cpm_nvbench()
+    rapids_cpm_nvbench( CPM_ARGS 
+                        OPTIONS
+                        "CMAKE_CXX_STANDARD 20"
+                        "CMAKE_CUDA_STANDARD 20")
     add_subdirectory(bench)
 endif()