I would probably avoid it if possible. Weed killer is pretty nasty stuff. It will likely be pretty diluted after some time and a good rain, but still probably not worth risk of ingesting any of it down the line.
I am unable to locate that brand of weed killer. Can you double check the brand? Or post the main ingredients. Typically it's better safe than sorry if you don't know what's in it.
Some weed killers become inactive once they have dried, and are safe. Others leave residual that you wouldn't want your dragon to be around.
I think I was able to find it. If it's what I found, it's main ingredient should be glyphosate, which is a common chemical for weed killers. It's typically low toxicity but that depends what other products are in it. Once dry it's safe to be around, however it binds to the soil. So if you are leaving your lawn as just a bunch of dirt, there will be traces of it in the dirt.
I would probably avoid it if possible. Weed killer is pretty nasty stuff. It will likely be pretty diluted after some time and a good rain, but still probably not worth risk of ingesting any of it down the line.