A Tower Controller reported they instructed an aircraft on short final to the runway but a vehicle holding short read it back and entered the runway. The Controller issued go-around instructions to the aircraft.

Narrative

I was working Local 1 during the afternoon field check with Airport Vehicle. Traffic was light; and the inspection was fairly routine. I fit Airport Vehicle in with the traffic to get them to bravo taxiway; west of Runway 35L. After clearing aircraft to land; I instructed Airport Vehicle to drive Runway 9L and hold short of Runway 35L. Airport Vehicle read it back correctly. After listening to the recording; when Aircraft X checked on; I instructed them to continue on their approach. Airport Vehicle read back 'continue on 35L;' but I did not catch the erroneous read back. I scanned my runway again as Aircraft X was 3/4-1/2 mile final and observed Airport Vehicle entering Runway 35L from Runway 9L. I immediately sent Aircraft X around to the left of the runway. When I did not get a response; I issued the go around again in which Aircraft X complied. The aircraft did not overfly the runway; and Airport Vehicle finished their inspection of Runway 35L. Be vigilant in all readback/hearbacks.