Start from MySQL 8.0.29 version changed charset support

https://dev.mysql.com/doc/relnotes/mysql/8.0/en/news-8-0-29.html
Important Note: The server now uses utf8mb3 rather than utf8 in the following cases:

• In the output of SHOW SQL statements (SHOW CREATE TABLE, SHOW CREATE VIEW, SHOW CREATE DATABASE)
• When reporting invalid strings.

Zabbix 4.0 supports only this charset:

// Default db and field character set
define('ZBX_DB_DEFAULT_CHARSET', 'UTF8');
define('ZBX_DB_MYSQL_DEFAULT_COLLATION', 'utf8_bin');

Steps to reproduce:

1. Install MySQL 8.0.29+ version
2. Create database
   create database zabbix character set utf8 collate utf8_bin;
3. Connect to database in user interface

Result: Cannot connect to the database. Incorrect default charset for Zabbix database: "utf8mb3" instead "UTF8".
Expected result: need to add utf8mb3 support