maintenance: Git config has a new syntax

nixos/home/development/git.nix

···
   programs = {
     git = {
       enable = true;
-      userName = "bpavuk";
-      userEmail = "[e-mail]";
+
+      settings = {
+        user.email = "[e-mail]";
+        user.name = "bpavuk";
+      };
     };
     gh.enable = true;
   };