flake.nix: Update nixpkgs: release-23.05 -> nixos-23.05-small

Flake lock file updates:

• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/9eb24edd6a0027fed010ccfe300a9734d029983c' (2023-11-01)
  → 'github:NixOS/nixpkgs/decdf666c833a325cb4417041a90681499e06a41' (2023-11-18)

Author: roberth

flake.lock

@@ -1,9 +1,7 @@
 {
   description = "The purely functional package manager";
 
-  # FIXME go back to nixos-23.05-small once
-  # https://github.com/NixOS/nixpkgs/pull/264875 is included.
-  inputs.nixpkgs.url = "github:NixOS/nixpkgs/release-23.05";
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-23.05-small";
   inputs.nixpkgs-regression.url = "github:NixOS/nixpkgs/215d4d0fd80ca5163643b03a33fde804a29cc1e2";
   inputs.lowdown-src = { url = "github:kristapsdz/lowdown"; flake = false; };
   inputs.flake-compat = { url = "github:edolstra/flake-compat"; flake = false; };