[Unity] downgrade cmake version requirement

[Hzfengsy]

The PR #16335 updated the CMakeLists.txt, setting the minimum version to be 3.24 for the compatibility of native CMAKE_CUDA_ARCHITECTURES.

However,

1. This breaks the CI on image Cortex-M and Hexagon on main branch.
2. The feature is only used when CUDA builds on AND undefined CMAKE_CUDA_ARCHITECTURES.

Hence, I move the version check logic inside the CUDA cmake file.

cc @vinx13 @tqchen