[CI][Neuron] Fail and exit on first error

[elaineyz]

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.

Purpose

Update the neuron buildkite script to fail on first errored file. This will prevent errors getting ignored silently.

Test Plan

I first ran the updated bash command locally to make sure all tests are still passing; next I temporarily modified one of the neuron test scripts to raise an arbitrary exception and verified that the command terminates immediately.

Test Result

See above

(Optional) Documentation Update

[github-actions[bot]]

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[elaineyz]

@DarkLight1337 / @simon-mo / @WoosukKwon can you help approve and merge this minor change? thanks!