update rocm version truncate

[kiran-thumma]

Rocm version truncate update
update vllm whls naming
old: vllm-0.16.1.dev8+ga903704c6.d20260316.rocm712-cp312-...whl
new: vllm-0.16.1.dev8+ga903704c6.d20260316.rocm7.12.0rc0-cp312-...whl

[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 ask your reviewers to trigger select CI tests on top of fastcheck CI.

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.

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