[2.x] Remove deprecation warning during setup for PHP 8.2

[halftrainedharry]

What does it do?

Adds the property $config to the class, so not to rely on dynamic properties.

Why is it needed?

In PHP 8.2 the deprecation warning

Deprecated: Creation of dynamic property modInstallLexicon::$config is deprecated in .../setup/includes/modinstalllexicon.class.php on line 35

may get shown on screen during the installation.

How to test

Install MODX with PHP 8.2 and display_errors = On and verify that the deprecation warning is not shown.

Related issue(s)/PR(s)

https://community.modx.com/t/error-message-on-upgrade-from-modx2-8-5-to-modx2-8-6/7099

[modxcommunity]

This pull request has been mentioned on MODX Community. There might be relevant details there:

https://community.modx.com/t/error-message-on-upgrade-from-modx2-8-5-to-modx2-8-6/7099/2