Update CUDA 12 handling (in light of move to CUDA 12.6)

[jakirkham]

As conda-forge has moved from CUDA 12.0 to CUDA 12.6 ( conda-forge/conda-forge-pinning-feedstock#6720 ), this means that this now builds with the latest CUDA 12 instead of the oldest.

When a similar change was needed for CUDA 11, we concluded that it was possible to build against CUDA 11 latest and install for older CUDA 11.x's ( #132 (comment) ).

So think we can adapt those changes for CUDA 12 to the same effect. Filing this to make those changes.

[jakirkham]

@conda-forge-admin , please re-render

[conda-forge-webservices]

Hi! This is the friendly automated conda-forge-webservice.

I just wanted to let you know that I started rerendering the recipe in #201.