fix(n8n): restructure version handling for nix-update compatibility

- Store version without 'n8n@' prefix (e.g., '2.8.3' not 'n8n@2.8.3')
- Construct tag with prefix: tag = "n8n@${version}"
- Update to version 2.8.3 with correct hashes

This allows nix-update to work correctly with the custom update.sh
script that strips the 'n8n@' prefix from GitHub release tags.

pkgs/n8n/default.nix

@@ -18,20 +18,20 @@
 }:
 stdenv.mkDerivation (finalAttrs: {
   pname = "n8n";
-  version = "n8n@2.7.5";
+  version = "2.8.3";
 
   src = fetchFromGitHub {
     owner = "n8n-io";
     repo = "n8n";
-    tag = finalAttrs.version;
-    hash = "sha256-tyTMlLqvI8i9WJa5J45q/ciD2EXtOwEnSoQ9VefKxO4=";
+    tag = "n8n@${finalAttrs.version}";
+    hash = "sha256-xbJZD+L/8ZK7GPqFKO6H/Cg40Pk2cqN3MWC+mNFVxbI=";
   };
 
   pnpmDeps = fetchPnpmDeps {
     inherit (finalAttrs) pname version src;
     pnpm = pnpm_10;
     fetcherVersion = 3;
-    hash = "sha256-s6l049slBJCP6qCgY/uLNuIVDNuUmiTUX94sKDi+86g=";
+    hash = "sha256-gX4pYiztKIRFbJNZhtQviWpp80teOzX1JaYKylGe4TY=";
   };
 
   nativeBuildInputs =