upload wheels to downloads.rapids.ai

[jameslamb]

After I merged #95, saw uploads to https://pypi.anaconda.org/rapidsai-wheels-nightly/simple/ fail like this:

jq: error (at <unknown>): Cannot iterate over null (null)
Using Anaconda API: https://api.anaconda.org/
Error:  ('Authentication token is missing. Please, use `anaconda login` to reauthenticate.', 401)

(build link

I forgot that the upload workflows still expect to find wheel artifacts in S3.
That'll change with rapidsai/shared-workflows#332 in the 25.08 release, but for now we still need to upload to S3.

This adds that upload, to hopefully fix publishing to https://pypi.anaconda.org/rapidsai-wheels-nightly/simple/

[jacobtomlinson]

Looks good