Update Available Rust versions for 24.04

According to https://launchpad.net/ubuntu/+source/rustc-1.85, Ubuntu 24.04 (Noble) has Rust 1.85.

We should update the documentation:

https://github.com/canonical/ubuntu-for-developers-docs/blob/c94c53e3071bb7e868965698627b709a776c1a20/docs/reference/availability/rust.md?plain=1#L23

There are also other Ubuntu versions that may be out-of-date.

Start with docs/reference/availability/rust.md, especially the linked table around line 23, and compare its Ubuntu 24.04 and other listed versions with the Rust packages on Launchpad. Update the entries that are out of date, and consider the issue complete when the documented versions match the current Ubuntu availability.

Written by the indexing model from the issue text.