fix: Conditionally include terminal-notifier in devenv.nix for macOS

Author: joscha

devenv.nix

@@ -16,11 +16,14 @@
     })
   ];
 
-  packages = [
-    pkgs.git
-    pkgs.terminal-notifier
-    pkgs.python312Packages.setuptools
-  ];
+  packages =
+    [
+      pkgs.git
+      pkgs.python312Packages.setuptools
+    ]
+    ++ lib.optionals pkgs.stdenv.isDarwin [
+      pkgs.terminal-notifier
+    ];
 
   languages.python.enable = true;
   languages.python.uv.enable = true;