fix(ci): restore auth for docs gh-pages deploy

[wgtmac]

No description provided.

[wgtmac]

@kevinjqliu I'm not sure if this is the right approach to fix https://github.com/apache/iceberg-cpp/actions/runs/24883794037/job/72858619932. I can only verify it by merging this PR.

[Copilot]

Pull request overview

Restores authenticated git access for the documentation deployment job so the workflow can push the generated site to the gh-pages branch from main.

Changes:

• Exposes GITHUB_TOKEN to the deploy step environment.
• Updates the origin remote URL to use token-based HTTPS authentication before pushing to gh-pages.

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[kevinjqliu]

great catch! this should work, similar to https://github.com/apache/iceberg/blob/main/.github/workflows/site-ci.yml

one nit: we can make the permissions more granular by moving contents: write to the job level, like so https://github.com/apache/iceberg/blob/f475ccb5c579b8a1d4842507b12e854161dea7af/.github/workflows/site-ci.yml#L30-L37

[wgtmac]

Thanks @kevinjqliu! I will explore that later. Let me fix this the breaking site first.