Fix permissions when building docs

[dhruvkb]

Description

This PR fixes the CI that was broken due to permission errors, arising presumably from merging #1013. The good news is that #1013 also contains the solution, supplying the DC_USER variable in the CI.

Checklist

• My pull request has a descriptive title (not a vague title like
  Update index.md).
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  a parent feature branch.
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• I added or updated tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible
  errors.

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[github-actions]

API Developer Docs Preview: Ready

https://wordpress.github.io/openverse-api/_preview/1055

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[AetherUnbound]

Ah, another one! Thanks for the quick fix 🚀