This was pretty annoying on rust release day, because it introduced
new warnings.
Specifically 1.73 introduced a spurious one about PartialOrd and Ord
disagreeing when both were in fact #derive-d.
- https://github.com/ATiltedTree/setup-rust has not been committed to since May
2022, I am uncertain about how widely used it is.
- It appears to have a bug with restoring its internal cache whenever there
comes a new stable version (immediate guess would be the cache-key does not
resolve `stable` to a specific version, which somehow breaks rustup, but I have not investigated)
- https://github.com/dtolnay/rust-toolchain is a more sensible take of https://github.com/actions-rs/toolchain,
where the original repo appears to be unmaintained.
It is implemented in one file of yaml/bash
https://github.com/dtolnay/rust-toolchain/blob/master/action.yml, we could
easily fork it if it becomes unmainted, unlike the other actions which uses
unnecessary javascript
