[CI] Upload plog to github artifact

[Potabk]

What this PR does / why we need it?

This patch upload the plog to GitHub artifacts if it exists, this will help developers view the plog to locate more detailed errors.

Does this PR introduce any user-facing change?

How was this patch tested?

• vLLM version: v0.11.0
• vLLM main: vllm-project/vllm@83f478b

[gemini-code-assist]

Note

Gemini is unable to generate a review for this pull request due to the file types involved not being currently supported.

[github-actions]

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[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.