[ci] simplify processing of `CMAKE_CUDA_FLAGS` variable in `CMakeLists.txt` (#4799)

* Update CMakeLists.txt

* Update cuda.yml

* Update CMakeLists.txt

* Update CMakeLists.txt

* Update cuda.yml

CMakeLists.txt

@@ -174,7 +174,7 @@ endif()
 if(USE_CUDA)
     find_package(CUDA 9.0 REQUIRED)
     include_directories(${CUDA_INCLUDE_DIRS})
-    LIST(APPEND CMAKE_CUDA_FLAGS -Xcompiler=${OpenMP_CXX_FLAGS} -Xcompiler=-fPIC -Xcompiler=-Wall)
+    set(CMAKE_CUDA_FLAGS "${CMAKE_CUDA_FLAGS} -Xcompiler=${OpenMP_CXX_FLAGS} -Xcompiler=-fPIC -Xcompiler=-Wall")
 
     set(CUDA_ARCHS "6.0" "6.1" "6.2" "7.0")
     if(CUDA_VERSION VERSION_GREATER_EQUAL "10.0")
@@ -189,14 +189,14 @@ if(USE_CUDA)
     list(POP_BACK CUDA_ARCHS CUDA_LAST_SUPPORTED_ARCH)
     list(APPEND CUDA_ARCHS "${CUDA_LAST_SUPPORTED_ARCH}+PTX")
     CUDA_SELECT_NVCC_ARCH_FLAGS(CUDA_ARCH_FLAGS ${CUDA_ARCHS})
+    string(REPLACE ";" " " CUDA_ARCH_FLAGS "${CUDA_ARCH_FLAGS}")
 
-    LIST(APPEND CMAKE_CUDA_FLAGS ${CUDA_ARCH_FLAGS})
+    set(CMAKE_CUDA_FLAGS "${CMAKE_CUDA_FLAGS} ${CUDA_ARCH_FLAGS}")
     if(USE_DEBUG)
       SET(CMAKE_CUDA_FLAGS "${CMAKE_CUDA_FLAGS} -g")
     else()
       SET(CMAKE_CUDA_FLAGS "${CMAKE_CUDA_FLAGS} -O3 -lineinfo")
     endif()
-    string(REPLACE ";" " " CMAKE_CUDA_FLAGS "${CMAKE_CUDA_FLAGS}")
     message(STATUS "CMAKE_CUDA_FLAGS: ${CMAKE_CUDA_FLAGS}")
 
     ADD_DEFINITIONS(-DUSE_CUDA)