nixos/nix-channel: fix editorconfig warnings and apply nixpkgs-fmt

nixos/modules/config/nix-channel.nix

@@ -3,8 +3,8 @@
   configuration to work.
 
   See also
-   - ./nix.nix
-   - ./nix-flakes.nix
+  - ./nix.nix
+  - ./nix-flakes.nix
  */
 { config, lib, ... }:
 let
@@ -28,9 +28,9 @@ in
             Whether the `nix-channel` command and state files are made available on the machine.
 
             The following files are initialized when enabled:
-             - `/nix/var/nix/profiles/per-user/root/channels`
-             - `/root/.nix-channels`
-             - `$HOME/.nix-defexpr/channels` (on login)
+              - `/nix/var/nix/profiles/per-user/root/channels`
+              - `/root/.nix-channels`
+              - `$HOME/.nix-defexpr/channels` (on login)
 
             Disabling this option will not remove the state files from the system.
           '';
@@ -48,7 +48,7 @@ in
             "nixos-config=/etc/nixos/configuration.nix"
             "/nix/var/nix/profiles/per-user/root/channels"
           ]
-          else [];
+          else [ ];
         defaultText = ''
           if nix.channel.enable
           then [