fix formatter error

agenix.nix

@@ -1,5 +1,4 @@
-{ machine, ...}:
-{
+{ machine, ... }: {
   age = {
     identityPaths = [ "/root/age_ed25519" ];
 

configuration.nix

@@ -32,7 +32,9 @@
         KbdInteractiveAuthentication = false;
       };
       extraConfig = ''
-        HostCertificate ${builtins.toFile "host_ed25519-cert.pub" machine.host-cert}
+        HostCertificate ${
+          builtins.toFile "host_ed25519-cert.pub" machine.host-cert
+        }
         HostKey ${config.age.secrets.host_ed25519.path}
       '';
     };
@@ -66,7 +68,9 @@
     };
 
     extraConfig = ''
-      CertificateFile ${builtins.toFile "user_ed25519-cert.pub" machine.user-cert}
+      CertificateFile ${
+        builtins.toFile "user_ed25519-cert.pub" machine.user-cert
+      }
       HostKey ${config.age.secrets.user_ed25519.path}
     '';
   };

flake.nix

@@ -39,8 +39,7 @@
         ];
       };
 
-      # TODO. if uncommented, nix flake check fails
-      # formatter = pkgs.nixfmt;
+      formatter.${system} = pkgs.nixfmt;
 
       nixosConfigurations = mkNixosSystems (machine: {
         inherit system;