RUST-577 Bump dependencies with dependabot

[isabelatkinson]

Here's an example PR from my fork: isabelatkinson#5, and a patch for those changes: https://spruce.mongodb.com/version/682bbb5f2a3ef700075f76b4/tasks?page=0&sorts=STATUS%3AASC%3BBASE_STATUS%3ADESC&variant=%5Ecompile%24.

This does the equivalent of running cargo update; i.e., it doesn't update the dependencies in Cargo.toml, as doing so may bump to a new major version requiring code changes and/or an MSRV update. Dependabot does allow configuring minor version bumps only, but this breaks for pre-1.0 dependencies, for which a minor version update (e.g. 0.2.0->0.3.0) can include breaking changes.

I chose a weekly cadence as I expect we should be able to merge these PRs as-is most of the time, but we can revisit if it becomes disruptive.

[isabelatkinson]

dependabot gets confused by the path dependency (https://github.com/mongodb/libmongocrypt-rust/blob/c333ab07e36f72ac3a4fd8c9f1ff96a98e60ea3e/mongocrypt/Cargo.toml#L21), so we'll need to update this dependency manually