Disable failing GPT-OSS Eval (Blackwell) for now (vllm-project#25107)

Signed-off-by: mgoin <mgoin64@gmail.com>
Signed-off-by: xuebwang-amd <xuebwang@amd.com>

Author: mgoin

.buildkite/test-pipeline.yaml

@@ -812,7 +812,7 @@ steps:
   timeout_in_minutes: 60
   working_dir: "/vllm-workspace/"
   gpu: b200
-  # optional: true
+  optional: true # disable while debugging
   source_file_dependencies:
   - tests/evals/gpt_oss
   - vllm/model_executor/models/gpt_oss.py