move to junk misfires because it is case-insensitive

The move to junk sieve rule is case insensitive by default, so instead of only matching 'Yes' in X-Spam-Status, it also matches 'BAYES_' and will misfire.

https://www.howtoforge.com/community/threads/change-to-sieve_filter-master-template-causes-all-mail-moved-to-junk.86744/