build: install Rust for CI builds

[deadprogram]

This PR installs Rust as part of the CI build for wasm32-unknown-unknown modules built by the mecha build command update in hybridgroup/mechanoid#27

[orsinium]

Nitpick: IDK why everyone adds name: for every step in Github Actions. You can omit it, and then Github Actions will show the executed command instead, which is in 95% of cases is readable enough.

[deadprogram]

You can omit it, and then Github Actions will show the executed command instead

Hmm I should do that in the future. Thanks!