Upgrade clippy's warnings to errors. (I'm assuming this is what you wanted, and it's just a bug that you don't have it set up that way, but I'm totally happy to undo this if you'd rather keep clippy as warning-only).
Run CI on a schedule so that if Rust updates and causes e.g. clippy or rustfmt problems, you get a notice.
Number 3 means if it starts failing, you get emails until it's fixed, but this avoids forcing contributors to touch/fix parts unrelated to their contribution, or having a busted master. (Personally, this has worked well for me, but maybe if you had a lot of crates it could start being a problem). All that said, I would not fault you if you don't more emails in your life.
Edit: Embarrassingly forgot to rename the PR title, whoops!
This:
Number 3 means if it starts failing, you get emails until it's fixed, but this avoids forcing contributors to touch/fix parts unrelated to their contribution, or having a busted master. (Personally, this has worked well for me, but maybe if you had a lot of crates it could start being a problem). All that said, I would not fault you if you don't more emails in your life.
Edit: Embarrassingly forgot to rename the PR title, whoops!