FrozenError: can't modify frozen String
https://sentry.gitlab.net/gitlab/gitlabcom/issues/586036/
FrozenError: can't modify frozen String
notify.rb:171:in `prepend'
headers[:subject]&.prepend('Re: ')
notify.rb:171:in `mail_answer_thread'
headers[:subject]&.prepend('Re: ')
emails/service_desk.rb:20:in `service_desk_new_note_email'
abstract_controller/base.rb:188:in `process_action'
send_action(method_name, *args)
abstract_controller/callbacks.rb:20:in `block in process_action'
super
...
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can't modify frozen String