Update rust

[bitdivine]

Motivation

The rust updater tries to update to the wrong version. It gets the latest release from GitHub, however that does not correspond to the latest stable version. In fact, it currently matches an older release that presumably had a patch release.

Changes

• Determine the latest stable version directly from the channel toml.
  • Note: This is the authoritative file used by rustup (see the code), rust-forge (see the code).

Tests

• This now generates a PR to update Rust to 1.72.1 instead of 1.71.1.

Todos

• Add entry to changelog (if necessary).

[lmuntaner]

Thanks!