FIG. 1 is a perspective view of a trigger actuator. FIG. 2 is a left side view of the trigger actuator shown in FIG. 1. FIG. 3 is a right side view of the trigger actuator shown in FIG. 1. FIG. 4 is a back view of the trigger actuator shown in FIG. 1. FIG. 5 is a top view of the trigger actuator shown in FIG. 1; and, FIG. 6 is a bottom view of the trigger actuator shown in FIG. 1. The broken lines represent unclaimed portions of the trigger actuator and form no part of the claimed design.