This story gets repeated every year and it never is a problem. It’s the yearly marketing stunt to end up in the “Bild” our trash tabloid.
So, they're not serious. If they had a real shortage, they'd be thrilled to buy back bottles at effectively ~8 cents per bottle (the amount they'd 'overpay' for old bottles sold with the original deposit). Cheaper and easier to ask the public to work for free returning more bottles despite inflation.