Nginx builder backends support

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This PR fixes a bug where CI tests for examples/backends would consistently fail. The nginx builder was not processing the backends configuration option, specifically failing to generate depends_on entries, which caused verification commands in the CI to fail. This change updates builders/nginx.js to correctly handle the backends configuration, ensuring the associated CI tests now pass.

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Automatically closed this PR because it was created by Bugbot autofix for #80, and that PR was closed.