[security][ci] Restrict privileged GPU jobs to trusted branches

[bvolpato]

Summary

• Run secret-bearing pull_request_target GPU jobs only for branches in this repository.
• Skip generic remote GPU jobs for fork pull requests, where repository credentials are unavailable.
• Keep push, manual dispatch, maintainer label, and draft gates unchanged.
• Remove the unsafe fork-checkout override from all five privileged workflows.

Why

The labeled GPU workflows check out and execute the pull request head while exposing repository Anyscale and Hugging Face credentials. A maintainer-applied label limits execution, but an external fork still controls the submitted scripts, config, and remote test payload.

The generic GPU workflow is not privileged on fork pull requests because GitHub withholds secrets, but it still starts and fails before tests with invalid Anyscale credentials. Skipping that job makes the missing GPU signal explicit instead of reporting a code failure.

External contributions must be mirrored to a reviewed branch in this repository before privileged GPU validation. Unprivileged CPU checks continue through their existing workflows.

Validation

• Parsed all changed workflows with yq.
• actionlint 1.7.12
• Event predicate truth tables covering push, manual dispatch, same-repo PRs, forks, drafts, and missing labels
• Coverage scan: all five pull_request_target GPU workflows guarded; no unsafe checkout override remains
• Generic fork GPU job resolves to skipped instead of submitting without credentials
• git diff --check

[gemini-code-assist]

Note

Gemini is unable to generate a review for this pull request due to the file types involved not being currently supported.