Run narwhals tests nightly. (#18093)

This enables narwhals tests in nightly CI.

Authors:
  - Bradley Dice (https://github.com/bdice)

Approvers:
  - Matthew Murray (https://github.com/Matt711)
  - Gil Forsyth (https://github.com/gforsyth)

URL: #18093

.github/workflows/test.yaml

@@ -168,3 +168,14 @@ jobs:
       date: ${{ inputs.date }}
       sha: ${{ inputs.sha }}
       script: "ci/test_cudf_polars_polars_tests.sh"
+  narwhals-tests:
+    secrets: inherit
+    uses: rapidsai/shared-workflows/.github/workflows/custom-job.yaml@branch-25.04
+    with:
+      build_type: ${{ inputs.build_type }}
+      branch: ${{ inputs.branch }}
+      date: ${{ inputs.date }}
+      sha: ${{ inputs.sha }}
+      node_type: "gpu-l4-latest-1"
+      container_image: "rapidsai/ci-conda:latest"
+      run_script: ci/test_narwhals.sh