Increase the # of downloader.rb's retry attempts

Apparently 9 was not enough either.
https://rubyci.org/logs/rubyci.s3.amazonaws.com/rhel_zlinux/ruby-master/log/20201123T063303Z.fail.html.gz

tool/downloader.rb

@@ -197,7 +197,7 @@ class Downloader
       $stdout.flush
     end
     begin
-      data = with_retry(9) do
+      data = with_retry(10) do
         url.read(options.merge(http_options(file, since.nil? ? true : since)))
       end
     rescue OpenURI::HTTPError => http_error