CI 3.x - How to set database connection collation?

Hello
I'm a bit confused as to how to set the database connection collation from within CodeIgniter 3.x. There is a dbcollat configuration parameter in the config, but it is not used for this purpose if you read the comment about it in the code and grep where it's used.
Since the default connection collation is utf8mb4_general_ci when used with the utf8mb4 character set in MariaDB 10.5, and I wanted to use utf8mb4_unicode_ci or utf8mb4_unicode_520_ci for my database, how do I set the connection collation from within CodeIgniter?
Thanks
Jamie