chore(nix): bump rust-overlay from 672fa5f to 5b5c521 (#83)

Bumps [rust-overlay](https://github.com/oxalica/rust-overlay) from `672fa5f` to `5b5c521`.
- [Commits](oxalica/rust-overlay@672fa5f...5b5c521)

---
updated-dependencies:
- dependency-name: rust-overlay
  dependency-version: 5b5c521d6cae9ef4aa32f888eb2c0ce595c9be52
  dependency-type: direct:production
...

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