flake: add nixf-diagnose to treefmt config

Checks nixd's diagnostic lints using libnixf.

tests/extra-args.nix

@@ -12,7 +12,7 @@ let
     };
   generated = makeNixvimWithModule {
     module =
-      { regularArg, extraModule, ... }:
+      { extraModule, ... }:
       {
         _module.args = {
           regularArg = "regularValue";

tests/main.nix

@@ -4,8 +4,6 @@
   lib ? pkgs.lib,
   linkFarm,
   pkgs,
-  self,
-  system,
   pkgsForTest,
 }:
 let

tests/test-sources/modules/dependencies.nix

@@ -27,12 +27,7 @@ in
     };
 
   all =
-    {
-      lib,
-      pkgs,
-      options,
-      ...
-    }:
+    { lib, options, ... }:
     let
       enableDep = depName: depOption: {
         enable = isDepEnabled depName depOption.package.default;

tests/test-sources/plugins/pluginmanagers/lz-n.nix

@@ -64,7 +64,7 @@ in
     };
 
   example-multiple-plugin =
-    { pkgs, lib, ... }:
+    { pkgs, ... }:
     {
       extraPlugins =
         with pkgs.vimPlugins;