Use GITHUB_TOKEN name instead of GITHUB_API_KEY

[pelikhan]

The GITHUB_TOKEN is the common name for the GitHub apis, set by default in codespaces.

agentic/packages/github/src/github-client.ts

Line 49 in 27599b7

apiKey = getEnv('GITHUB_API_KEY')

[pelikhan]

This is a breaking change; but you could also support both.

[stevepeak]

Thank you for sharing @pelikhan — I'll be addressing these issues shortly as I get more involved with Agentic 🙏