A pint in 5 gallons? 1:40? I would just run it. The tractor won't know the difference.
I've read that Mercedes recommended adding gas to diesel to help extreme cold weather starting. You might Google on that to see what proportion they recommended.
The two fuels are near identical. Gasoline evaporates to vapor near room temperature, while diesel has a higher vapor point. Gasoline is blended to resist ping, while ping is what makes diesel ignite. (Also diesel has slightly more energy per gallon; irrelevant here).
The only disadvantage I can see is that the volatile gas fumes raise your fire hazard up similar to that of an automobile. If you park it in your basement next to the water heater pilot light this might be a concern.
Just run it.