If you take this objection seriously, then you should also take issue with predictions like "nobody will ever transmit information faster than the speed of light", or things like it. After all, you can never actually observe the laws of physics to have been stable and universal for all time.

If nothing else, you can consider each as being a compact specification of an infinite sequence of testable predictions: "doesn't halt after one step", "doesn't halt after two steps",... "doesn't halt after n steps".