Update Nix flake (#36857)

Automated changes by the
[update-flake-lock](https://github.com/DeterminateSystems/update-flake-lock)
GitHub Action.

```
Flake lock file updates:

• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/dd9b079' (2026-02-27)
  → 'github:nixos/nixpkgs/aca4d95' (2026-03-06)
```

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