feat: use new option for commit signing

nix/users/luca/git.nix

@@ -2,12 +2,14 @@
   enable = true;
   userName = "rocketcamel";
   userEmail = "luca_lise@icloud.com";
+  signing = {
+    signByDefault = true;
+    format = "ssh";
+    key = "~/.ssh/commits.id_rsa.pub";
+  };
   extraConfig = {
     init = {
       defaultBranch = "main";
     };
-    commit.gpgsign = true;
-    gpg.format = "ssh";
-    user.signingkey = "~/.ssh/commits.id_rsa.pub";
   };
 }

nix/users/luca/home.nix

@@ -1,4 +1,4 @@
-{ config, pkgs, ... }:
+{ config, pkgs, lib, ... }:
 
 {
   home.username = "luca";