build(deps): bump nixpkgs-stable in /internal

Bumps [nixpkgs-stable](https://github.com/NixOS/nixpkgs) from `fcb8fcd` to `5880666`.
- [Commits](NixOS/nixpkgs@fcb8fcd...5880666)

---
updated-dependencies:
- dependency-name: nixpkgs-stable
  dependency-version: 5880666fd9eb563038431edb35c2d0aa595884e6
  dependency-type: direct:production
...

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Author: dependabot[bot]