Consider checking crates.io links

[tzerrell]

(As discussed here: https://github.com/risc0/risc0/pull/370#issuecomment-1421654920)

We currently have broken links on https://crates.io/crates/risc0-zkvm/0.12.0. We could probably create a weekly or manual link checker for our crates.io crates by adapting https://github.com/risc0/website/blob/main/.github/workflows/action.yml. (Weekly because this can only be tested post-release, and releases are less frequent than weekly.)