treewide: Format all Nix files

Format all Nix files using the officially approved formatter,
making the CI check introduced in the previous commit succeed:

  nix-build ci -A fmt.check

This is the next step of the of the [implementation](https://github.com/NixOS/nixfmt/issues/153)
of the accepted [RFC 166](https://github.com/NixOS/rfcs/pull/166).

This commit will lead to merge conflicts for a number of PRs,
up to an estimated ~1100 (~33%) among the PRs with activity in the past 2
months, but that should be lower than what it would be without the previous
[partial treewide format](https://github.com/NixOS/nixpkgs/pull/322537).

Merge conflicts caused by this commit can now automatically be resolved while rebasing using the
[auto-rebase script](8616af08d9/maintainers/scripts/auto-rebase).

If you run into any problems regarding any of this, please reach out to the
[formatting team](https://nixos.org/community/teams/formatting/) by
pinging @NixOS/nix-formatting.

nixos/modules/programs/git.nix

@@ -1,4 +1,9 @@
-{ config, lib, pkgs, ... }:
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
 
 let
   cfg = config.programs.git;
@@ -19,27 +24,43 @@ in
           let
             gitini = attrsOf (attrsOf anything);
           in
-          either gitini (listOf gitini) // {
-            merge = loc: defs:
+          either gitini (listOf gitini)
+          // {
+            merge =
+              loc: defs:
               let
-                config = builtins.foldl'
-                  (acc: { value, ... }@x: acc // (if builtins.isList value then {
-                    ordered = acc.ordered ++ value;
-                  } else {
-                    unordered = acc.unordered ++ [ x ];
-                  }))
-                  {
-                    ordered = [ ];
-                    unordered = [ ];
-                  }
-                  defs;
+                config =
+                  builtins.foldl'
+                    (
+                      acc:
+                      { value, ... }@x:
+                      acc
+                      // (
+                        if builtins.isList value then
+                          {
+                            ordered = acc.ordered ++ value;
+                          }
+                        else
+                          {
+                            unordered = acc.unordered ++ [ x ];
+                          }
+                      )
+                    )
+                    {
+                      ordered = [ ];
+                      unordered = [ ];
+                    }
+                    defs;
               in
               [ (gitini.merge loc config.unordered) ] ++ config.ordered;
           };
         default = [ ];
         example = {
           init.defaultBranch = "main";
-          url."https://github.com/".insteadOf = [ "gh:" "github:" ];
+          url."https://github.com/".insteadOf = [
+            "gh:"
+            "github:"
+          ];
         };
         description = ''
           Configuration to write to /etc/gitconfig. A list can also be