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/gpt-bios-compat.nix

@@ -14,7 +14,7 @@
             start = "0";
             end = "1M";
             part-type = "primary";
-            flags = ["bios_grub"];
+            flags = [ "bios_grub" ];
           }
           {
             name = "root";