flake: treefmt-nix follow nixpkgs

Flake lock file updates:

• Updated input 'treefmt-nix/nixpkgs':
    'github:nixos/nixpkgs/0591d6b57bfeb55dfeec99a671843337bc2c3323' (2023-02-04)
  → follows 'nixpkgs'

flake.lock

@@ -137,22 +137,6 @@
         "type": "indirect"
       }
     },
-    "nixpkgs_3": {
-      "locked": {
-        "lastModified": 1675545634,
-        "narHash": "sha256-TbQeQcM5TA/wIho6xtzG+inUfiGzUXi8ewwttiQWYJE=",
-        "owner": "nixos",
-        "repo": "nixpkgs",
-        "rev": "0591d6b57bfeb55dfeec99a671843337bc2c3323",
-        "type": "github"
-      },
-      "original": {
-        "owner": "nixos",
-        "ref": "nixos-unstable",
-        "repo": "nixpkgs",
-        "type": "github"
-      }
-    },
     "nur-update": {
       "inputs": {
         "nixpkgs": [
@@ -230,7 +214,9 @@
     },
     "treefmt-nix": {
       "inputs": {
-        "nixpkgs": "nixpkgs_3"
+        "nixpkgs": [
+          "nixpkgs"
+        ]
       },
       "locked": {
         "lastModified": 1675588998,

flake.nix

@@ -34,6 +34,7 @@
     disko.inputs.nixpkgs.follows = "nixpkgs";
 
     treefmt-nix.url = "github:numtide/treefmt-nix";
+    treefmt-nix.inputs.nixpkgs.follows = "nixpkgs";
   };
 
   outputs = inputs @ { flake-parts, ... }: