Bump REXML to 3.3.9 for Ruby 3.3 (ruby#11972)

Author: ajmyers01

gems/bundled_gems

@@ -9,7 +9,7 @@ minitest        5.20.0  https://github.com/minitest/minitest
 power_assert    2.0.3   https://github.com/ruby/power_assert
 rake            13.1.0  https://github.com/ruby/rake
 test-unit       3.6.1   https://github.com/test-unit/test-unit
-rexml           3.3.6   https://github.com/ruby/rexml
+rexml           3.3.9   https://github.com/ruby/rexml
 rss             0.3.1   https://github.com/ruby/rss
 net-ftp         0.3.4   https://github.com/ruby/net-ftp
 net-imap        0.4.9.1   https://github.com/ruby/net-imap