Remove mention to csv fixtures from test_helper in guides [ci skip]

guides/code/getting_started/test/test_helper.rb

@@ -3,7 +3,7 @@
 require 'rails/test_help'
 
 class ActiveSupport::TestCase
-  # Setup all fixtures in test/fixtures/*.(yml|csv) for all tests in alphabetical order.
+  # Setup all fixtures in test/fixtures/*.yml for all tests in alphabetical order.
   #
   # Note: You'll currently still have to declare fixtures explicitly in integration tests
   # -- they do not yet inherit this setting