I will add a "me too" to the first 2 replies, live with it till warranty is out.
When that is over get the mower up nice & high and you will find a little white plunger switch that activates when the mower is put into reverse.
Usually they are normally open ( closes when plunger is depressed ) , if so pull the plug off & tape it over .
Stick a bit of tape under the hood with a message to remind you to reconnect it when you sell it or you will leave yourself open to legal action should a latter owner come to grief.
OTOH if the switch is normally closed, then get a pair of spade terminals, make a small jumper to bridge the plug then tape over as previously suggested.
Be careful to make sure it is the correct switch, there are 3 small switches under the mower and the wrong one disconnected will give you real grief.
With JD I always suggest you get your hands on the JD Technical Manual they are worth 10 times what JD asks for them & will pay for themselves in hard cash or hours of your time the first time you use it.
In the electrical section they show you exactly where each & every switch is, how it is wired in a schematic and where the lug is that connects it to the wiring.
Should you sell the mower 2nd hand including the technical manual will nearly double the sale price.
I found this out by accident so now buy a tech manual for every JD I sell which always go within the first week and I get $ 300 to $ 500 more for the mower than the general used price.