"Oh well, I'm glad that's settled then. Have a lovely wedding."
^^ This, as I think it doesn't draw you in further.
But I would love to deliberately misunderstand, and say something like: "Misunderstanding? I don't think there can be - you've just said it's not that big of a deal. I agree - your wedding isn't that big of a deal, and so I'm not that keen to give up loads of my time for it. I've got some important bits and pieces to be getting on with. But enjoy it anyway!