maintainers: add rvarago

maintainers/maintainer-list.nix

···
     githubId = 506953;
     name = "Ruud van Asseldonk";
   };
+  rvarago = {
+    email = "[e-mail]";
+    github = "rvarago";
+    githubId = 7365864;
+    name = "Rafael Varago";
+  };
   rvl = {
     email = "[e-mail]";
     github = "rvl";