only use a single nixpgks revision as input

flake.lock

@@ -3,7 +3,9 @@
     "esp-idf": {
       "inputs": {
         "flake-utils": "flake-utils",
-        "nixpkgs": "nixpkgs"
+        "nixpkgs": [
+          "nixpkgs"
+        ]
       },
       "locked": {
         "lastModified": 1758247379,
@@ -38,22 +40,6 @@
       }
     },
     "nixpkgs": {
-      "locked": {
-        "lastModified": 1759735786,
-        "narHash": "sha256-a0+h02lyP2KwSNrZz4wLJTu9ikujNsTWIC874Bv7IJ0=",
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "rev": "20c4598c84a671783f741e02bf05cbfaf4907cff",
-        "type": "github"
-      },
-      "original": {
-        "owner": "NixOS",
-        "ref": "nixos-25.05",
-        "repo": "nixpkgs",
-        "type": "github"
-      }
-    },
-    "nixpkgs_2": {
       "locked": {
         "lastModified": 1759558742,
         "narHash": "sha256-0IQRQijNKweSTrGXNOHWhKpZWUPrWdyaO31IziPU7wY=",
@@ -71,7 +57,7 @@
     "root": {
       "inputs": {
         "esp-idf": "esp-idf",
-        "nixpkgs": "nixpkgs_2",
+        "nixpkgs": "nixpkgs",
         "systems": "systems_2"
       }
     },