I incorrectly assumed Dependabot can find the Cargo config files, however, the projects must be specified independently (see: dependabot/dependabot-core#2178).

Without this, Dependabot fails with the following error:

```
Dependabot couldn't find a Cargo.toml

Dependabot requires a Cargo.toml to evaluate your Rust dependencies. It had expected to find one at the path: /src/Cargo.toml.

If this isn't a Rust project, you may wish to disable updates for it in the .github/dependabot.yml config file in this repo.
```

See: https://github.com/adeira/universe/network/updates/91435760