fix: use ****** format for GitHub API auth in fetch.ts

[Copilot]

The core-ci build task was failing with HTTP 403 on all GitHub API requests to download built-in extensions (ms-vscode.js-debug, ms-vscode.js-debug-companion, ms-vscode.vscode-js-profile-table).

Root Cause

build/lib/fetch.ts was constructing the Authorization header incorrectly:

// Before — encodes only the token; GitHub Basic auth requires base64(username:password)
ghApiHeaders.Authorization = 'Basic ' + Buffer.from(process.env.GITHUB_TOKEN).toString('base64');

Without a username: prefix, GitHub can't parse the credential and rejects the request with 403. The error message in the logs ("you may be rate limited") is added by the fetch wrapper whenever it sees a 403, masking the real cause.

Fix

// After — correct OAuth2 ****** for GitHub Actions tokens and PATs
ghApiHeaders.Authorization = 'Bearer ' + process.env.GITHUB_TOKEN;

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• https://api.github.com/repos/microsoft/vscode/actions/jobs/68598610598/logs
  • Triggering command: /usr/bin/gh gh api repos/microsoft/vscode/actions/jobs/68598610598/logs (http block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

Fix the failing GitHub Actions workflow "Code OSS / Compile & Hygiene (pull_request)".
Analyze the workflow logs, identify the root cause of the failure, and implement a fix.
Job ID: 68598610598
Job URL: /microsoft/vscode/actions/runs/23560432186/job/68598610598?pr=304877

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