Apply upstream default charset change

[tianon]

See WordPress/WordPress@08d1cf7

utf8mb4 is the complete UTF-8 implementation in MySQL, supporting the full range of Unicode characters by using up to 4 bytes per character. This includes characters outside the Basic Multilingual Plane, such as emoji and supplementary characters. utf8mb4 ensures full compatibility with modern text content and diverse character sets.

As of WordPress 4.2, on both new and existing installations, WordPress would automatically upgrade database tables to utf8mb4 on compatible servers (MySQL 5.5.3 or later). However, the default DB_CHARSET value during setup was still set to utf8 for compatibility with older MySQL versions.

As of WordPress 6.5, the minimum required MySQL version is 5.5.5, so the default can be updated to utf8mb4.

(We're currently on WordPress 6.8 here, but this default arguably makes sense to us much further back because we only support non-EOL MySQL versions.)

[yosifkit]

LGTM

To get the new default, users will need to remove wp-config.php from their WordPress volume so that the entrypoint will create a new one (but that will change your AUTH_KEY and other unique keys and salts if they aren't already passed via environment variables).

Or users can just set -e WORDPRESS_DB_CHARSET=utf8mb4 on their docker run.

[tianon]

Indeed -- but also, WordPress will have already upgraded their databases in-place. 😂 🤘