virtualboxExtpack: add friedrichaltheide to maintainers

pkgs/applications/virtualization/virtualbox/extpack.nix

···
     description = "Oracle Extension pack for VirtualBox";
     license = licenses.virtualbox-puel;
     homepage = "https://www.virtualbox.org/";
-    maintainers = with maintainers; [ sander ];
+    maintainers = with maintainers; [ sander friedrichaltheide ];
     platforms = [ "x86_64-linux" ];
   };
 }