fix ci workflow warnings

[nwagner84]

This PR uses dtolnay/rust-toolchain to setup the Rust toolchain. This fixes the deprecation warnings like:

build (ubuntu-latest, beta)
The following actions uses node12 which is deprecated and will be forced to run on node16: actions-rs/toolchain@v1. For more info: https://github.blog/changelog/2023-06-13-github-actions-all-actions-will-run-on-node16-instead-of-node12-by-default/

[dguo]

Thank you!

[dguo]

I was confused at first why this uses @master, but I see the docs say:

When passing an explicit toolchain as an input instead of @Rev, you'll want to use "dtolnay/rust-toolchain@master" as the revision of the action.