Make actionview ready for frozen strings

actionview/lib/action_view/renderer/streaming_template_renderer.rb

+# frozen_string_literal: true
 require "fiber"
 
 module ActionView
@@ -31,7 +32,7 @@ def log_error(exception)
           logger = ActionView::Base.logger
           return unless logger
 
-          message = "\n#{exception.class} (#{exception.message}):\n"
+          message = "\n#{exception.class} (#{exception.message}):\n".dup
           message << exception.annoted_source_code.to_s if exception.respond_to?(:annoted_source_code)
           message << "  " << exception.backtrace.join("\n  ")
           logger.fatal("#{message}\n\n")