Consider adding per CTK major.minor optional dependencies?

[leofang]

I actually want these jobs if possible, yes, but I can't do so with the existing [all] notation for installing the latest CUDA wheels (we let them float and do not add version constraints). To support testing CUDA 12.0 wheels it'd mean we need to add more optional tags like [cu120]. We could consider this in the future, but I am hesitant to do so now.

And without the extra tags, these jobs are redundant because it's the latest (12.6) wheels being installed for testing, which has been covered by other jobs.

Originally posted by @leofang in #393 (comment)