fix: preserve GitHub Actions env for prerelease provenance

[patrickkabwe]

Summary

• keep GitHub Actions detection available during pre-release publish so npm provenance can be generated
• override GITHUB_REF for semantic-release branch detection instead of unsetting GITHUB_ACTIONS

Verification

• git diff --check
• targeted workflow inspection confirmed no remaining env -u GITHUB_ACTIONS, both release paths override GITHUB_REF, and NPM_CONFIG_PROVENANCE remains enabled

Summary by CodeRabbit

• Chores
  • Updated the pre-release automation to use the configured pre-release branch reference for both actual and dry-run releases.

[coderabbitai]

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Run ID: f50dd9dc-146f-440c-b0fd-62a443267806

📥 Commits

Reviewing files that changed from the base of the PR and between d11ec5a and 3771809.

📒 Files selected for processing (1)

• .github/workflows/pre-release.yml

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[github-actions]

🎉 This PR is included in version 3.8.0-next.1 🎉

The release is available on:

• npm package (@next dist-tag)
• GitHub release

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