maintainers: add gardspirito

maintainers/maintainer-list.nix

···
     githubId = 20208;
     name = "Rok Garbas";
   };
+  gardspirito = {
+    name = "gardspirito";
+    email = "[e-mail]";
+    github = "gardspirito";
+    githubId = 29687558;
+  };
   garrison = {
     email = "[e-mail]";
     github = "garrison";