reduce duplication in rapids-get-pr-* scripts

[jameslamb]

Contributes to https://github.com/rapidsai/build-infra/issues/237

For a long time now, we've had tools in this project to make it easier to use one project's CI artifacts in another project's CI:

• rapids-get-pr-conda-artifact
• rapids-get-pr-wheel-artifact

Today, those download files from the downloads.rapids.ai S3 bucket. So when the GitHub Actions artifact storage stuff was first rolling out, #152 introduced GitHub-y versions of those:

• rapids-get-pr-conda-artifact-github
• rapids-get-pr-wheel-artifact-github

Now that all RAPIDS projects are uploading conda packages and wheels to the GitHub Actions artifact store, it's safe to remove those *-github scripts and just change the behavior of the others to use the GitHub Actions artifact store instead of S3.

Notes for Reviewers

Is it safe to merge this?

Yes. These scripts are not used in any long-lived CI.

GitHub search: https://github.com/search?q=%2Frapids%5C-get%5C-pr%2F%20AND%20NOT%20is%3Aarchived&type=code

They're only used temporarily on PRs during testing. See the docs where that's described: https://github.com/rapidsai/docs/blob/00878de8b9afead0f8d44221c228fda2dbbbd97e/resources/github-actions.md?plain=1#L186-L188

How I tested this

Created an rmm PR using this branch's gha-tools: rapidsai/rmm#1909

And then a cudf PR using this branch's gha-tools and the packages produced by CI from that rmm PR: NVIDIA/cudf#18747

Checked logs to confirm that the downloaded rmm packages were used:

• branch-25.06 testing: WIP: [DO NOT MERGE] test gha-tools changes NVIDIA/cudf#18747 (comment)
• branch-25.08 testing: WIP: [DO NOT MERGE] test gha-tools changes NVIDIA/cudf#18747 (comment)

[bdice]

Nice! All this makes sense. Thanks especially for your writeup on "Is this safe to merge?" because I had to think about that for a bit.