Fix doc build - run cargo metadata with --offline & --no-deps

[Wumpf]

What

• solves regression: docs.rs no longer showing docs for rerun 0.20 #8165
  (don't close ticket yet, have to confirm that docs.rs actually works)

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using examples from latest main build: rerun.io/viewer
  • Using full set of examples from nightly build: rerun.io/viewer
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG
• If applicable, add a new check to the release checklist!
• If have noted any breaking changes to the log API in CHANGELOG.md and the migration guide

• PR Build Summary
• Recent benchmark results
• Wasm size tracking

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To deploy documentation changes immediately after merging this PR, add the deploy docs label.

[teh-cmc]

Let's see how that goes before merging anything: https://github.com/rerun-io/rerun/actions/runs/11897219343