chore: avoid extra request when checking for MUSL builds

[SimenB]

Description

Avoid the extra network call per version as we have all the info needed from the index.json file.

Motivation and Context

See #2031

Testing Details

// tested in repl which has TLA
const { Octokit } = require('@octokit/rest');

const github = new Octokit();

const { data: unofficialBuildsIndexText } = await github.request('https://unofficial-builds.nodejs.org/download/release/index.json');

const buildVersion = unofficialBuildsIndexText.find(indexVersion => indexVersion.version === 'v20.0.0');

console.log(buildVersion?.files.includes('linux-x64-musl'));
console.log(buildVersion?.security);

Example Output(if appropriate)

Types of changes

• [ ] Documentation
• [ ] Version change (Update, remove or add more Node.js versions)
• [ ] Variant change (Update, remove or add more variants, or versions of variants)
• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [x] Other (none of the above)

Checklist

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING.md document.
• [x] All new and existing tests passed.

[SimenB]

(I'll land this after today's security release, just in case it messes something up)