feat: Add PHP 8.5 support

[LinnyTheDuck]

Description

Adding support for the PHP-8.5 container.

Testing Instructions

1. Check out this pull request
2. Build the PHP-8.5 container: tbuild PHP-8.5
3. Up the container: tup PHP-8.5
4. Test that you can load a T20 site and that you get deprecation notices.
5. Add an entry for totara85 in your debug server list in PHPStorm.
6. Add a break point in /login/index.php
7. Check that the break point is triggered when visiting http://integration.totara85.debug.localhost/login/index.php

Checklist

• Does what the author says it will do
• Testing instructions are provided
• Commit messages make sense and follow the conventional commit standard
• No identified security issues
• No identified maintenance issues
• Any third-party libraries/dependencies use the MIT or Apache 2.0 license
• Changes made are backwards compatible and will not break existing setups
• Changes to scripts in the bin/ directory run correctly on both MacOS and WSL
• Changes to containers can be built locally sucessfully (e.g. via tbuild container && tup container)
• Containers/images are compatible with both AMD64 (Windows) and ARM64 (MacOS)
• Changes made to config.php are compatible with our oldest supported Totara version, our newest Totara version, and Moodle

[markmetcalfe]

Looking good - will need to wait until the new MSSQL driver is out and update the Dockerfile