bulk_create not compatible with mariadb

Describe the bug
Using bulk_create to insert and update values on mariadb causes incompatible sql code to be generated

To Reproduce

   users = [
        model.User(user_id="1",name="James",email="james@email.com"),
        model.User(user_id="2",name="Claire",email="claire@email.com")
    ]

    await model.User.bulk_create(users, update_fields=["name","email"], on_conflict="user_id", batch_size=3)

Expected behavior
The SQL generated and passed is:

INSERT INTO `user` (`user_id`,`name`,`email`) VALUES ('1','James','james@email.com') 
    AS `new_User` ON DUPLICATE KEY UPDATE `name`='email',`name`='email'

(as it happens I am not sure why name=email is listed twice when I would expect name=name, email=email - so not even sure this would completely work on mysql)

But, on mariadb, the syntax needed is:

INSERT INTO `user` (`user_id`,`name`,`email`) VALUES ('1','James','james@email.com') 
     ON DUPLICATE KEY UPDATE `name`=VALUES(name),`email`=VALUES(email)

Additional context
Mysql 8 has deprecated VALUES - it does work, but gives a warning (as I understand it), this might require a dialect configuration. Or accept that VALUES works on both mysql and mariadb, even though it generates a warning on mysql

Start at the bulk_create implementation and the SQL generation path for MySQL-compatible databases, then reproduce the supplied example against MariaDB. Done means bulk_create with update_fields and on_conflict produces valid MariaDB SQL with the correct column mappings, while preserving appropriate MySQL behavior; add or run coverage for this case if the existing test layout is found.