chore(nix): bump rust-overlay from 02f536e to 40b0a3a

Bumps [rust-overlay](https://github.com/oxalica/rust-overlay) from `02f536e` to `40b0a3a`.
- [Commits](oxalica/rust-overlay@02f536e...40b0a3a)

---
updated-dependencies:
- dependency-name: rust-overlay
  dependency-version: 40b0a3a193e0840c76174b4a322874c8f6dd0a63
  dependency-type: direct:production
...

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