Update lib/fluent/plugin/in_windows_eventlog2.rb

`key=` not needed

Co-authored-by: Daijiro Fukuda <[email protected]>
Signed-off-by: Blake Hensley <[email protected]>

Author: BlakeHensleyy

lib/fluent/plugin/in_windows_eventlog2.rb

@@ -404,7 +404,7 @@ def parse_desc(record)
     end
 
     def to_key(key)
-      key = key.downcase! if @downcase_description_keys
+      key.downcase! if @downcase_description_keys
       key.gsub!(' '.freeze, @description_word_delimiter)
       key
     end