Specify Accept header for toolcache.downloadTool

[mbg]

Fixes a bug with #3110, where we missed setting this header for toolcache.downloadTool that's needed to get the actual artifact, rather than the JSON metadata.

Better solution than #3119, since browser_download_url is intended for use by browsers.

Risk assessment

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• Low risk: Changes are fully under feature flags, or have been fully tested and validated in pre-production environments and are highly observable, or are documentation or test only.

Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows.
• Consider adding a changelog entry for this change.
• Confirm the readme and docs have been updated if necessary.

[Copilot]

Pull Request Overview

This PR fixes a bug where the toolcache.downloadTool function was not properly downloading artifacts from GitHub releases due to a missing Accept header. The change adds the application/octet-stream header to ensure the actual binary artifact is downloaded instead of JSON metadata.

• Adds the required Accept: application/octet-stream header to toolcache.downloadTool calls
• Fixes the issue introduced in PR #3110 where downloads were returning metadata instead of actual artifacts

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/start-proxy-action.ts	Adds Accept header configuration to downloadTool call for proxy binary download
lib/start-proxy-action.js	Generated JavaScript version of the TypeScript changes

[mbg]

Successfully tested that this also works with the fallback in #3121: https://github.com/github/codeql-action/actions/runs/17805925098?pr=3121

[henrymercer]

Thanks for testing the fallback method!