flake.nix: update nix-darwin to 25.11, remove nixpkgs_25_11

Flake lock file updates:

• Updated input 'darwin':
    'github:LnL7/nix-darwin/000eadb231812ad6ea6aebd7526974aaf4e79355' (2025-10-03)
  → 'github:LnL7/nix-darwin/e95de00a471d07435e0527ff4db092c84998698e' (2025-11-26)
• Updated input 'darwin/nixpkgs':
    follows 'nixpkgs_25_05'
  → follows 'nixpkgs'
• Removed input 'nixpkgs_25_05'

Author: mweinelt

flake.lock

@@ -28,7 +28,6 @@
     };
 
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.11-small";
-    nixpkgs_25_05.url = "github:NixOS/nixpkgs/nixos-25.05-small";
     nixpkgs-unstable.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
 
     flake-parts = {
@@ -37,8 +36,8 @@
     };
 
     darwin = {
-      url = "github:LnL7/nix-darwin/nix-darwin-25.05";
-      inputs.nixpkgs.follows = "nixpkgs_25_05";
+      url = "github:LnL7/nix-darwin/nix-darwin-25.11";
+      inputs.nixpkgs.follows = "nixpkgs";
     };
 
     flake-utils.url = "github:numtide/flake-utils";