actions-rs actions are unmaintained

[jku]

All GitHub actions in the actions-rs org are archived and unmaintained. We should stop using them.

• Uses of actions-rs/cargo look like they would be trivial to replace with just calling cargo with uses
• I'm not familiar enought with toolchain to say if just using rustup is a decent replacement?

[jku]

I'm not familiar enought with toolchain to say if just using rustup is a decent replacement?

Looks like plain rustup would work. We may still want to add something like https://github.com/Swatinem/rust-cache but as far as I can tell this is a separate thing: current actions don't do caching either.

[flavio]

There's also https://github.com/dtolnay/rust-toolchain which is gained popularity. Unfortunately the releases are not tagged and there's no plan to start doing that (see this issue)

[jku]

There's also https://github.com/dtolnay/rust-toolchain which is gained popularity.

Yes, I considered a couple of alternatives but at least so far I've not found much reason to not just "do it manually" and avoid the dependency.