Utfmb4 instead of utf8mb3? (#442)

[regis]

@iamCristYe

BTW, when looking into the dumped mysql, I noticed the commands at tutor/local.rst at v12.0.1 · overhangio/tutor · GitHub will dump mysql internal tables like information_schema as well, which may not be desirable. What do you think? I’d be happy to make a PR.

I have a naive question: why is that not desirable?