actions-rs/toolchain unmaintained

[pentamassiv]

The actions-rs/toolchain Action has been unmaintained for a while now (actions-rs/toolchain#216). Github displays the following warning in workflows using it:
Node.js 12 actions are deprecated. For more information see: https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/. Please update the following actions to use Node.js 16: actions-rs/toolchain
It is probably a good idea to replace the Action.

A seemingly popular alternative is dtolnay/rust-toolchain