flake: treefmt-nix follow nixpkgs unstable

flake.lock

@@ -1222,22 +1222,6 @@
         "type": "github"
       }
     },
-    "nixpkgs_3": {
-      "locked": {
-        "lastModified": 1735554305,
-        "narHash": "sha256-zExSA1i/b+1NMRhGGLtNfFGXgLtgo+dcuzHzaWA6w3Q=",
-        "owner": "nixos",
-        "repo": "nixpkgs",
-        "rev": "0e82ab234249d8eee3e8c91437802b32c74bb3fd",
-        "type": "github"
-      },
-      "original": {
-        "owner": "nixos",
-        "ref": "nixpkgs-unstable",
-        "repo": "nixpkgs",
-        "type": "github"
-      }
-    },
     "pre-commit-hooks": {
       "inputs": {
         "flake-compat": "flake-compat_2",
@@ -1585,7 +1569,9 @@
     },
     "treefmt-nix": {
       "inputs": {
-        "nixpkgs": "nixpkgs_3"
+        "nixpkgs": [
+          "nixpkgs-unstable"
+        ]
       },
       "locked": {
         "lastModified": 1739829690,

flake.nix

@@ -15,7 +15,10 @@
 
     flake-parts.url = "github:hercules-ci/flake-parts";
 
-    treefmt-nix.url = "github:numtide/treefmt-nix";
+    treefmt-nix = {
+      url = "github:numtide/treefmt-nix";
+      inputs.nixpkgs.follows = "nixpkgs-unstable";
+    };
 
     # this is nice so one-off impure scripts can interact with attributes in
     # this flake