Require @rexml@ gem for ruby >= 3.0 (#37249).

Patch by Holger Just.


git-svn-id: https://svn.redmine.org/redmine/trunk@21635 e93f8b46-1217-0410-a6f0-8f06a7374b81

Gemfile

@@ -13,6 +13,7 @@ gem 'marcel'
 gem "mail", "~> 2.7.1"
 gem 'csv', '~> 3.2.0'
 gem 'nokogiri', '~> 1.13.6'
+gem "rexml", require: false if Gem.ruby_version >= Gem::Version.new('3.0')
 gem 'i18n', '~> 1.10.0'
 gem "rbpdf", "~> 1.20.0"
 gem 'addressable'