Replace unmaintained actions-rs/* actions in CI workflows

[striezel]

Basically all of the actions-rs/* actions are unmaintained. See actions-rs/toolchain#216 for more information. Due to their age they generate several warnings in CI runs, for example in https://github.com/RustCrypto/stream-ciphers/actions/runs/3596661836:

Node.js 12 actions are deprecated. For more information see: https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/. Please update the following actions to use Node.js 16: actions-rs/toolchain@v1, actions-rs/cargo@v1

To get rid of some of those warnings the occurrences of actions-rs/toolchain are replaced by dtolnay/rust-toolchain, and the occurrences of actions-rs/cargo are replaced by direct invocations of cargo.