docs: clarify github token configuration

[jjangga0214]

Issue for this PR

Closes #23487

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Updates the GitHub docs to match the current action interface. The docs previously referred to a token option and showed github_token in the workflow example, but the action uses use_github_token and reads the token from GITHUB_TOKEN.

How did you verify your code works?

Compared the docs against github/action.yml and packages/opencode/src/cli/cmd/github.ts to confirm the current action inputs and environment variable handling.

Screenshots / recordings

Not applicable.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search results, here are potentially related PRs:

Related PRs Found:

1. PR #23475 - "fix(installation): respect GITHUB_TOKEN/GH_TOKEN for GitHub API release check"

   • Related because it also deals with GITHUB_TOKEN configuration

2. PR #17225 - "fix(github): skip assertPermissions when use_github_token is true"

   • Directly related as it references the use_github_token flag mentioned in PR docs: clarify github token configuration #23488

3. PR #18881 - "docs(web): clarify GitHub token usage"

   • Related as another docs PR about GitHub token usage

These PRs are contextually related to the GitHub token configuration topic, though they appear to address different aspects. PR #23488 is specifically documentation clarification, while the others are fixes or other docs improvements around the same feature area.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍