actions-rs/toolchain is an "Unofficial GitHub Actions for Rust programming language" which has only one person in the organization, @svartalf, which appears to be MIA for a long time.
People are asking in vain for these fixes, check actions-rs/toolchain#221 (almost a year long).

There are a bunch of warnings in CI, e.g. https://github.com/rust-bitcoin/rust-bitcoin/actions/runs/6440479240/job/17492350278#step:5:46.

dtolnay/rust-toolchain is by a well-established Rust developer, and it is well-maintaned (and has more stars than actions-rs/toolchain.

It might be an easy fix, but we need to check if the options are semantically the same.