fix: Prevent Xdebug from triggering when running composer

[LinnyTheDuck]

Description

This disables XDebug when composer commands are run, as otherwise PHPStorm will attempt to resolve a breakpoint to a path that does not exist within the Totara project (i.e. /usr/bin/composer is not in the Totara project). This means running install/install_phpunit/install_behat will run without triggering breakpoints.

Testing Instructions

1. Run a shell in one of the PHP debug containers - e.g. tzsh php-8.3-debug
2. Turn on listen for connections in PHPStorm
3. Run install_behat
4. Observe that you get an error in PHPStorm that it can't resolve the path to /usr/bin/composer
5. Check out this pull request
6. Run a new shell in one of the PHP debug containers - e.g. tzsh php-8.3-debug
7. Run install_behat
8. Observe that the command runs fine without triggering any breakpoints

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