Fix vLLM LKG version

[ShobhitBehl]

Description

Fix and bump vLLM LKG version to d9408ffba3c8da5e289b5695d507707afce10a2f

• [Feat][Executor] Introduce RayExecutorV2 vllm#36836: Move WORKER_SPECIFIC_ENV_VARS to ray_utils.
• [Perf] Remove redundant device copies for CPU-only pooling token IDs, 48.9% E2E throughput improvement vllm#38139: Add prompt_token_ids_cpu to arguments of PoolingMetadata.

Tests

• CI

Checklist

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• I have performed a self-review of my code.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have made or will make corresponding changes to any relevant documentation.

[github-actions]

Description

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Checklist

Before submitting this PR, please make sure:

• I have performed a self-review of my code.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have made or will make corresponding changes to any relevant documentation.