set_architectures output correct CUDA arch values for RAPIDS mode

[robertmaynard]

Description

In RAPIDS mode the local variable CMAKE_CUDA_ARCHITECTURES still was set to OFF and not the updated value. Corrected the code to update the local instance of the variable always before output.

Checklist

• [x] I am familiar with the Contributing Guidelines.
• [x] New or existing tests cover these changes.
• [x] The documentation is up to date with these changes.
• [x] The cmake-format.json is up to date with these changes.

[robertmaynard]

/merge