Ensure date-check cron job is using latest stable Rust
Ensure date-check cron job is using latest stable Rust

This should prevent future failures like this one [1].

[1]: https://github.com/rust-lang/rustc-dev-guide/runs/4067460927?check_suite_focus=true

rust-lang/rustc-dev-guide,rust-lang/rustc-dev-guide,rust-lang/rustc-dev-guide,rust-lang/rustc-dev-guide