Update actions/checkout action and replace unmaintained actions-rs actions

[taiki-e]

• Update actions/checkout action
• Use cargo directly instead of unmaintained actions-rs/cargo action
• Use dtolnay/rust-toolchain instead of unmaintained actions-rs/toolchain action

See also https://github.com/tokio-rs/tokio/pull/5316 for the context of unmaintained actions and alternatives.