maintainers.lenny: add github (#437479)

maintainers/maintainer-list.nix

···
   };
   lenny = {
     name = "Lenny.";
+    github = "LennyPenny";
+    githubId = 4027243;
     matrix = "@lenny:flipdot.org";
     keys = [ { fingerprint = "6D63 2D4D 0CFE 8D53 F5FD  C7ED 738F C800 6E9E A634"; } ];
   };