style: Re-apply style normalisation

Originally this was manually applied with;

```sh
nixpkgs-fmt **.nix && statix fix
```

but I overlooked the fact that `**.nix` would only expand to files in
the root (I should have used `**/*.nix`).

Previous commit adds `nix fmt` support which passes `.` to `nixpkgs-fmt`
(if no other path is explicitly specified when running `nix fmt`).

This commit includes the changes made by running `nix fmt`.

example/stand-alone/configuration.nix

@@ -1,8 +1,8 @@
-{
-  pkgs,
-  lib,
-  ...
-}: let
+{ pkgs
+, lib
+, ...
+}:
+let
   # We just import from the repository for testing here:
   disko = import ../../. {
     inherit lib;
@@ -41,7 +41,8 @@
       };
     };
   };
-in {
+in
+{
   imports = [
     (disko.config cfg)
   ];