[4.x] Invalid get index 'ml_options'

https://github.com/GodotModding/godot-mod-loader/pull/536 introduced settings for game version validation:

https://github.com/GodotModding/godot-mod-loader/blob/39f6059a9ef15be179ed0ea800a7da6f7c715e7e/addons/mod_loader/resources/mod_manifest.gd#L116-L123

It includes a reference to `ml_options`, which causes the error below because `ModLoaderStore` is not available in the editor context.

`res://addons/mod_loader/resources/mod_manifest.gd:116 - Invalid get index 'ml_options' (on base: 'Node (mod_loader_store.gd)').`