Your 'best' line is that it is a new symptom of your engine. It didn't use this amount earlier.
It probably still is an 'acceptable' amount of usage to fall within acceptable operating parameters to avoid having to warranty it.
Grumpy explained it all pretty well. Your options aren't great, fight GM, sell it, fix it, add a quart between oil changes.
For what its worth, EVERY vehicle I've ever done an oil change on has had less oil come out in the drain pan than what gets dumped back in. Usually about a quart. Regardless of make, age, mileage, use, etc.
Not calling anyone out, arguing/fighting anyone, but if you tell me yours doesn't use a drop, my first response is BS until I see you measure out the drain pan.