The ornamental design for a step for a truck, as shown and described.
FIG. 1 is a left-front perspective view of a step for a truck;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is a cross sectional view through the line 8-8 in FIG. 6 thereof.
The step for a truck is shown with a symbolic break in its length. The appearance of any portion of the article between the break lines forms no part of the claimed design. The broken lines shown in FIG. 7 and FIG. 8 illustrate the inner structure of the step that forms no part of the claimed design.