Fix collation issue when using LOWER with REGEXP

[jayktaylor]

When using REGEXP (e.g titleregexp in a DPL invocation) in combination with LOWER (e.g ignorecase in a DPL invocation), the following error is received:

[DynamicPageList4] Query error at MediaWiki\Extension\DynamicPageList4\Query::buildAndSelect - Dpl: Error 3995: Character set 'utf8mb4_0900_ai_ci' cannot be used in conjunction with 'binary' in call to regexp_like.
Function: MediaWiki\Extension\DynamicPageList4\Query::buildAndSelect - Dpl
Query: SELECT /*+ MAX_EXECUTION_TIME(10000)*/ DISTINCT p.page_namespace AS `page_namespace`,p.page_id AS `page_id`,p.page_title AS `page_title`  FROM `page` `p`    WHERE ((LOWER(CAST(p.page_title AS CHAR CHARACTER SET utf8mb4)) REGEXP '(.*[cc]aves*_[(]+)') OR (LOWER(CAST(p.page_title AS CHAR CHARACTER SET utf8mb4)) REGEXP '(.*[cc]aves*$)')) AND p.page_is_redirect = 0  LIMIT 500  

This PR fixes this issue by using the correct collation.

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