Use dtolnay/rust-toolchain instead of actions-rs/toolchain

[jannic]

This fixes some warning emitted by github actions:

[warning]The `set-output` command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

Also, actions-rs/toolchain looks deprecated, the repo at https://github.com/actions-rs/toolchain is archived.