Test with Config Split 1.x and Config Ignore 2.x

Note that for Config Ignore there is a weird message that shows up in the UI at least, see ✨ Misleading message on "admin/config/development/configuration" about configurations handled via config_overlay Active .

I did see some issues with the old Config Split on a project, but didn't investigate yet, so possibly the resolution here will be just to add a Composer conflict with the older versions, but not sure yet.