Build/Test Tools: Fix bug pulling local environment containers on Apple silicone.

The MySQL Docker containers for versions 5.7 and below do not support recent Apple silicone chips. Previously this was fixed by including `amd64/` as a prefix to the image name in the `docker-compose.yml` file (see [54096]). However, this stopped working after recent updates to Docker Desktop.

This changeset removes the `amd64/` prefix for the image used as the database container and raises the default version of MySQL in the local development environment to the current LTS version (8.0). Because this version is still maintained, there are `arm64` containers available to use.

This also documents a new workaround for contributors looking to run the local Docker environment using MySQL 5.7 or earlier, which entails creating a small `docker-compose.override.yml`.

Props bernhard-reiter, johnbillion, afragen, huzaifaalmesbah.
Fixes #59930.
Built from https://develop.svn.wordpress.org/trunk@57568


git-svn-id: http://core.svn.wordpress.org/trunk@57069 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.5-alpha-57567';
+$wp_version = '6.5-alpha-57568';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.