buildkite: fix GitHub status after build-pr retry

[reakaleek]

What

• Move GitHub commit status updates from a separate teardown step into the build-pr job lifecycle
• Post pending when build-pr starts and success or failure when it finishes, including on retries

Why

• When a user retries a failed build-pr step, Buildkite only reruns that step
• The teardown step already ran and does not rerun, so GitHub keeps the old failure status even when the build passes

Notes

• The early build-pr-setup step still posts pending while the GCP agent starts
• Status posting failures do not fail the build

Made with Cursor

[github-actions]

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