BUG: `./ci/tools/download-wheels` does not exist in the backport branch

[leofang]

When releasing 12.9.3 the upload job failed in the last step (uploading wheels to git archive):

/home/runner/work/_temp/8d380c3d-0ade-4875-a288-9859bce7d985.sh: line 2: ./ci/tools/download-wheels: No such file or directory

https://github.com/NVIDIA/cuda-python/actions/runs/18389027457/job/52394720524

This happens because I released on the main branch with the git tag v12.9.3, but the release-upload.yml workflow assumes that the needed scripts live in the same branch as the git tag, which is the 12.9.x branch, and we did not backport the needed PR #873 to this branch.

I am not sure how to fix this, but also it is not the end of the world not having wheels archived with GitHub Release. We only added this capability very recently. We just need to figure out how to fix it before the next release.

[leofang]

For posterity here are the failed runs:

• cuda-bindings 12.9.3 -> testpypi: https://github.com/NVIDIA/cuda-python/actions/runs/18389027457
• cuda-bindings 12.9.3 -> pypi: https://github.com/NVIDIA/cuda-python/actions/runs/18389397458
• cuda-python 12.9.3 -> testpypi: https://github.com/NVIDIA/cuda-python/actions/runs/18389514030
• cuda-python 12.9.3 -> pypi: https://github.com/NVIDIA/cuda-python/actions/runs/18389643856