Adapt to changes in Config Ignore 3.x

Is anyone already working on this?

@kevin.pfeifer Not yet - I'm currently working on a release for another contrib module. Collaboration is welcome :-)

Tests passing so merging to tag a 2.2.0-beta1 so that it's easier to test on sites given the change in composer requirements.

Discussed with @bircher in Slack and we think this should do it.

Automatically closed - issue fixed for 2 weeks with no activity.