Retain Qwen3-Omni documentation audio for failure diagnosis

Signed-off-by: tzhouam <tzhouam@connect.ust.hk>

.buildkite/cuda/test-nightly.yml

@@ -48,6 +48,8 @@ steps:
       - label: ":full_moon: Omni · Doc Test with H100 · 2-GPU"
         source_file_dependencies: omni_qwen3_omni_doc
         timeout_in_minutes: 90
+        artifact_paths:
+          - audio_*.wav
         commands:
           - pytest -s -v tests/examples/ -m "full_model and omni and H100 and B200 and cards_2" --run-level "full_model"