libuv: disable tty_pty test on darwin

pkgs/development/libraries/libuv/default.nix

···
         "tcp_open" "tcp_write_queue_order" "tcp_try_write" "tcp_writealot"
         "multiple_listen" "delayed_accept"
         "shutdown_close_tcp" "shutdown_eof" "shutdown_twice" "callback_stack"
+        "tty_pty"
       ];
     tdRegexp = lib.concatStringsSep "\\|" toDisable;
     in lib.optionalString doCheck ''