remove some unnecessary libcudf nightly builds (#16714)

Follow-up to #16650 and #15483.

`libcudf` wheels are identical (same content, same filename) across Python versions, but due to an oversight in the PRs linked above, we're currently building nightlies of them once per Python version supported by RAPIDS 😭 

You can see this on recent runs of the `build` workflow:

<img width="752" alt="image" src="https://github.com/user-attachments/assets/ba3a2192-1752-4d32-a79b-6f238fae9f18">

([build link](https://github.com/rapidsai/cudf/actions/runs/10627299703/job/29460218854))

This PR fixes that by applying the same matrix filter to `libcudf` nightly build jobs as is currently applied to PR jobs:

https://github.com/rapidsai/cudf/blob/5e420ff63ba2997a37bf5dfbfaa73c5f05225f9d/.github/workflows/pr.yaml#L195-L200

Authors:
  - James Lamb (https://github.com/jameslamb)

Approvers:
  - Kyle Edwards (https://github.com/KyleFromNVIDIA)
  - Bradley Dice (https://github.com/bdice)

URL: #16714

.github/workflows/build.yaml

@@ -71,6 +71,8 @@ jobs:
     secrets: inherit
     uses: rapidsai/shared-workflows/.github/workflows/[email protected]
     with:
+      # build for every combination of arch and CUDA version, but only for the latest Python
+      matrix_filter: group_by([.ARCH, (.CUDA_VER|split(".")|map(tonumber)|.[0])]) | map(max_by(.PY_VER|split(".")|map(tonumber)))
       build_type: ${{ inputs.build_type || 'branch' }}
       branch: ${{ inputs.branch }}
       sha: ${{ inputs.sha }}

.github/workflows/pr.yaml

@@ -197,6 +197,7 @@ jobs:
     secrets: inherit
     uses: rapidsai/shared-workflows/.github/workflows/[email protected]
     with:
+      # build for every combination of arch and CUDA version, but only for the latest Python
       matrix_filter: group_by([.ARCH, (.CUDA_VER|split(".")|map(tonumber)|.[0])]) | map(max_by(.PY_VER|split(".")|map(tonumber)))
       build_type: pull-request
       script: "ci/build_wheel_libcudf.sh"