[CI] Fix FlashInfer AOT in release docker image

[mgoin]

Purpose

FlashInfer has shifted to using FLASHINFER_CUDA_ARCH_LIST in recent releases https://docs.flashinfer.ai/installation.html#python-package

This has resulted in the 0.10.2 release not having prebuilt flashinfer binaries

See buildkite log https://buildkite.com/organizations/vllm/pipelines/release/builds/8688/jobs/0199833c-09e7-46fe-a38a-6dd9493547e5/log#117-11445

[2025-09-25T23:59:38Z] #33 8.381 RuntimeError: Please explicitly set env var FLASHINFER_CUDA_ARCH_LIST.

Test Plan

Test Result

Successful (long) release image build here https://buildkite.com/vllm/release/builds/8709/steps/canvas?sid=019986dd-f571-4207-abb3-4c61a3b010da

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Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

[gemini-code-assist]

Code Review

This pull request fixes an issue with FlashInfer's Ahead-Of-Time (AOT) compilation in the release Docker image by setting the required FLASHINFER_CUDA_ARCH_LIST environment variable. The changes correctly enable AOT compilation via a build argument and update the Dockerfile to use the new environment variable. My review includes one suggestion to ensure the list of CUDA architectures is correctly formatted as a semicolon-separated string, as required by FlashInfer's documentation, to prevent potential build issues.