Update to Rust 1.76

[emilk]

• Part of Tracking issue: Speed up CI #3033

What

I discovered the cargo doc step in our CI was taking over 7 minutes due to some bug in cargo doc. Updating Rust fixes this.

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 newly built examples: rerun.io/viewer
  • 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!

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

[github-actions]

Deployed docs

Commit	Link
6144539	https://landing-8yps6zzqf-rerun.vercel.app/docs

[teh-cmc]

The cross-platform image is on its way; ill have a look at the CI failure in the mean time.

[Wumpf]

happens too often? ah well

[emilk]

More than twice, at this is too fun to fix this cycle :)

[teh-cmc]

I have no idea why the web check is failing, except that it's related to sccache. There is a long history of issues of that nature between cargo tooling and sccache.

I'll disable it for now since @Wumpf is already refactoring it on another branch, and then we should be able to merge this.