Air carrier First Officer reported receiving an aircraft terrain caution during descent into RNO. The Captain immediately stopped the descent; the caution disappeared; and the flight crew continued the landing.

Narrative

RNO night; weather was VMC. We set up for the 17R approach KLOCK transition. Reno Approach said that the longer Runway 17R was not available. Approach asked us what approach we wanted for 17L. We chose the RNAV 17L. By the time the Captain loaded the new approach we were already slightly above profile. We both identified this and the Captain started down while I made a PA to the passengers and finished the Before Landing Checklist. When we re-intercepted the path; we believe the pilot flying forgot to activate VNAV. So we continued slightly below path. This resulted in a caution terrain just after the fix WORTH on the RNO RNAV 17L. Captain immediately stopped the descent and the caution immediately disappeared. We continued and landed without further incident.Cause: Late runway change at destination. Pilot monitoring - me - failing to trap the Captain error of not re-engaging VNAV.Suggestions: Be more aware of what VNAV mode aircraft is in even during high workload phases of flight. Try to trap and correct all pilot flying errors.