Fix regression from refactoring NotificationFactory::Template#to_s

lib/notification_factory/template.rb

@@ -24,10 +24,11 @@ examples how to use
     # some browsers start adding HTML tags
     # fixes https://github.com/zammad/zammad/issues/385
     @template.gsub(/\#\{\s*t\((.+?)\)\s*\}/m) do
-      if $1 =~ /^'(.+?)'$/
+      content = $1
+      if content =~ /^'(.+?)'$/
         %(<%= t "#{strip_content($1)}", #{@escape} %>)
       else
-        %(<%= t d"#{strip_variable(strip_content($1))}", #{@escape} %>)
+        %(<%= t d"#{strip_variable(content)}", #{@escape} %>)
       end
     end.gsub(/\#\{\s*config\.(.+?)\s*\}/m) do
       %(<%= c "#{strip_variable($1)}", #{@escape} %>)