ci: use dtolnay/rust-toolchain instead of #1

Job	Run time
cargo fmt --all -- --check	10s
cargo check (ubuntu-latest)	23s
Code Coverage (ubuntu-latest, unix)	2m 1s
cargo check (macOS-latest)	1m 55s
cargo clippy -- -D warnings (ubuntu-latest)	23s
Code Coverage (macos-latest, macos)	1m 24s
cargo check (windows-latest)	1m 55s
cargo clippy -- -D warnings (macOS-latest)	39s
Code Coverage (windows-latest, windows)	1m 49s
cargo test (ubuntu-latest)	32s
cargo clippy -- -D warnings (windows-latest)	34s
cargo test (macOS-latest)	52s
cargo test (windows-latest)	1m 1s
	13m 38s

Provide feedback