[ticket/12873] Test the correct identifier in \phpbb\db\tools

https://tracker.phpbb.com/browse/PHPBB3-12873
https://tracker.phpbb.com/browse/PHPBB3-12770

PHPBB3-12770
PHPBB3-12873
I guess in this case its better to have two different names. It's unlikely that we aant to drop the index later anyway