CI test linux://doc:source/llm/doc_code/serve/multi_gpu/dp_pd_example is consistently_failing

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CI test linux://doc:source/llm/doc_code/serve/multi_gpu/dp_pd_example is consistently_failing. Recent failures:
- https://buildkite.com/ray-project/postmerge/builds/14268#019a623d-3f13-42ca-b23a-b3fd63398c76
- https://buildkite.com/ray-project/postmerge/builds/14268#019a6213-415c-419e-ae37-d35690b1b69f

DataCaseName-linux://doc:source/llm/doc_code/serve/multi_gpu/dp_pd_example-END
Managed by OSS Test Policy

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This test is now considered as flaky because it has been failing on postmerge for too long. Flaky tests do not run on premerge.

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Test passed on latest run: https://buildkite.com/ray-project/postmerge/builds/14398#019a850d-3db3-4a99-bb77-e831176002dc