build(deps): bump nixos-stable from 8eeec93 to a311611 in /tests

Bumps [nixos-stable](https://github.com/NixOS/nixpkgs) from `8eeec93` to `a311611`.
- [Commits](https://github.com/NixOS/nixpkgs/commits)

---
updated-dependencies:
- dependency-name: nixos-stable
  dependency-version: a3116115851d68b8952a2a4221cc25a84e56b532
  dependency-type: direct:production
...

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Author: dependabot[bot]