[ci] add b200 test placeholder

[simon-mo]

Add B200 Test Demo

• Needs: add b200 queue ci-infra#131

Example Build
https://buildkite.com/vllm/ci/builds/25339/steps/canvas?jid=0198589f-bccc-4b20-b539-3305e07a2849

[github-actions]

👋 Hi! Thank you for contributing to the vLLM project.

💬 Join our developer Slack at https://slack.vllm.ai to discuss your PR in #pr-reviews, coordinate on features in #feat- channels, or join special interest groups in #sig- channels.

Just a reminder: PRs would not trigger full CI run by default. Instead, it would only run fastcheck CI which starts running only a small and essential subset of CI tests to quickly catch errors. You can run other CI tests on top of those by going to your fastcheck build on Buildkite UI (linked in the PR checks section) and unblock them. If you do not have permission to unblock, ping simon-mo or khluu to add you in our Buildkite org.

Once the PR is approved and ready to go, your PR reviewer(s) can run CI to test the changes comprehensively before merging.

To run CI, PR reviewers can either: Add ready label to the PR or enable auto-merge.

🚀

[gemini-code-assist]

Code Review

This pull request introduces a new CI test step for the Blackwell GPU architecture. The intention is good, but the implementation has a couple of areas for improvement. My review focuses on making the new test step clearer, more robust, and more effective at validating the target hardware.

[gemini-code-assist]

This test command has two significant issues:

1. Lack of Specificity: The test is labeled "Blackwell Test" but runs a generic example without any Blackwell-specific configurations. To be a meaningful test for the new architecture, it should validate features unique to Blackwell, such as FP8 data types. Please consider adding arguments to enable and test such features (e.g., --dtype float8_e4m3fn).
2. Implicit Dependency: The command relies on the default model (meta-llama/Llama-3.2-1B-Instruct) hardcoded in examples/offline_inference/basic/chat.py. This makes the CI step fragile. To make the test more robust and self-contained, the model should be specified explicitly as a command-line argument.

    - python3 examples/offline_inference/basic/chat.py --model meta-llama/Llama-3.2-1B-Instruct --dtype float8_e4m3fn # Or other Blackwell-specific args

[gemini-code-assist]

The optional: true setting is commented out, which creates ambiguity about the intended behavior of this test step. If this step should not block the pipeline on failure, this line should be uncommented. If the step is mandatory, this commented-out line should be removed to improve clarity and prevent future confusion.