If it ever gets to court it would be tossed out on summary judgment. Unless it is in front of a wacko liberal judge. The restaurant is not a government entity of any sort. It does not force anybody to do anything. Their promotion isn’t a law either. Hey atheist idiot.....go to hell.
One would hope it would be tossed out, but don’t be too sure! Remember the photograhper who refused to work for a lesbian couple that was getting “married”. They took her to court and won a settlement. We have lost our freedom of association. When the government started saying you could not discriminate, it quickly evolved to mean you have lost your freedom to decide with whom you will do business.