tests : disable backend sampler hip multi output (#26878)

tests : disable backend sampler hip multi output (#26878)

* test-backend-sampler: skip multi_output_sampling_chain on HIP

The new multi_output_sampling_chain test uses top_k, whose backend probs
path needs CUB (unavailable on HIP), so sampled_probs is null and the test
aborts. Add it to the existing HIP skip list alongside the other TOP_K tests.

* ci: keep gpu-rocm logs in a per-run dir keyed by GitHub run id

The self-hosted gpu-rocm runner can't upload logs to Azure blob (egress
firewalled), so a run's logs were wiped by the next run. Write each run's
logs to $OUT/run-<run_id>-<attempt>/ so an Actions run URL maps to its logs.

* test-backend-sampler: also skip multi_output_cpu on HIP

Like the other TOP_K-based subtests, multi_output_cpu's backend sampler
never initializes on HIP (no CUB TOP_K), so it aborts. Add it to the skip list.

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Co-authored-by: Jim Wu <redacted>