Add rexml as a gem dependency (#4768)

* Add rexml as a gem dependency

Rexml is no longer included with Ruby 3+, we therefore need to add the dependency explicitely.

* Remove garbage character from test file

Author: Pierre Nespo

activemerchant.gemspec

@@ -26,6 +26,7 @@ Gem::Specification.new do |s|
   s.add_dependency('builder', '>= 2.1.2', '< 4.0.0')
   s.add_dependency('i18n', '>= 0.6.9')
   s.add_dependency('nokogiri', '~> 1.4')
+  s.add_dependency('rexml', '~> 3.2.5')
 
   s.add_development_dependency('mocha', '~> 1')
   s.add_development_dependency('pry')

test/unit/gateways/payflow_test.rb

@@ -1144,7 +1144,7 @@ def xpath_prefix_for_transaction_type(tx_type)
 
   def threeds_xpath_for_extdata(attr_name, tx_type: 'Authorization')
     xpath_prefix = xpath_prefix_for_transaction_type(tx_type)
-    %(string(#{xpath_prefix}/PayData/ExtData[@Name='#{attr_name}']/@Value)")
+    %(string(#{xpath_prefix}/PayData/ExtData[@Name='#{attr_name}']/@Value))
   end
 
   def authorize_buyer_auth_result_path