ci: fix opencode workflow auth setup for branch pushes

[Jordonbc]

Motivation

• The opencode workflow was failing to push fix branches with remote: Duplicate header: "Authorization" because the runner kept a persisted git credential while the opencode action also supplied a token.

Description

• Set persist-credentials: false on the actions/checkout@v6 step and enabled use_github_token: true for both the primary and fallback anomalyco/opencode/github steps in .github/workflows/opencode.yml so the action consistently manages GitHub auth.

Testing

• Ran git diff --check which reported no issues and committed the change as ci: fix opencode git auth configuration, and the modification is a CI workflow-only fix (no application code changes).

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Codex Task

[github-actions]

Review Summary: Looks good

The changes are correct and address the duplicate Authorization header issue:

1. persist-credentials: false - Prevents the checkout action from persisting the runner's GitHub token to .git/credentials, which was causing the conflict with the opencode action's own token handling.

2. use_github_token: true - Tells the opencode action to use its own authentication mechanism, ensuring consistent token management across both primary and fallback steps.

Minor observations:

• The GITHUB_TOKEN env var on lines 40 and 52 may be redundant if use_github_token: true makes the action self-contained, but it doesn't hurt and provides flexibility.
• The fix follows the workflow's existing patterns and conventions.

No issues found. This is a clean, targeted CI fix.

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