When OpenCV is built with CUDA as a first class language (ENABLE_CUDA_FIRST_CLASS_LANGUAGE) the root to the CUDA toolkit is defined as CUDAToolkit_LIBRARY_ROOT by CMake.

I forgot to include this change in #23021 meaning that currently the python bindings fail to load when OpenCV is built with CUDA as a first class language (i.e. import cv2 fails with ImportError: DLL load failed while importing cv2: The specified module could not be found.).

This is fixed in this PR.

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• The PR is proposed to the proper branch
• There is a reference to the original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake