Fix JetBrains GitHub token resolution

[jdubois]

Description:
Resolve GitHub authentication for JetBrains Runtime release discovery from the action token input first, with GITHUB_TOKEN retained as a fallback. Releases API pagination now keeps the same authentication and requests GitHub JSON media; requests remain unauthenticated when neither token source is set.

The shared token resolver is also used by the existing GitHub-hosted manifest headers. Generated dist bundles are included.

Related issue:
Fixes #1221

Check list:

• Ran npm run check locally (format, lint, build, test) and all checks pass.
• Documentation changes are not required.
• Tests were added or updated to cover the changes.

[Copilot]

Pull request overview

This pull request fixes GitHub authentication for JetBrains Runtime release discovery by resolving credentials from the action token input first (with GITHUB_TOKEN as a fallback), and ensuring the same authentication headers are used consistently across paginated GitHub Releases API requests while negotiating JSON responses.

Changes:

• Introduces a shared getGitHubToken() utility to centralize token resolution (token input → GITHUB_TOKEN fallback).
• Updates JetBrains Runtime release discovery to use the shared resolver, preserve auth across pagination, and request GitHub JSON media.
• Adds/updates unit tests covering token precedence, fallback behavior, and omission of auth when no token is available (and includes regenerated dist bundles).

Show a summary per file

File	Description
src/util.ts	Adds shared getGitHubToken() and reuses it in GitHub header construction.
src/distributions/jetbrains/installer.ts	Uses shared token resolver and JSON Accept header for paginated GitHub Releases API calls.
tests/distributors/jetbrains-installer.test.ts	Adds coverage for token input precedence, env fallback, and unauthenticated behavior across pagination.
dist/setup/index.js	Regenerated bundle reflecting the shared token resolver usage.
dist/setup/282.index.js	Regenerated JetBrains-related bundle reflecting token/header changes.
dist/cleanup/index.js	Regenerated bundle reflecting the shared token resolver export/use.

Review details

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• Files reviewed: 3/6 changed files
• Comments generated: 0
• Review effort level: Lite