The ornamental design for a packingbox, as shown and described.
FIG. 1 is a front perspective view of a packing box showing our new design in a closed configuration;
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 top plan view of the packing box, showing our new design in a flat configuration.
In FIGS. 1, 2, and 8, the broken lines surrounding the solid line perimeter depict a feature of the packaging box that forms no part of the claimed design. All the sides except the front side depict portions of the packaging box that form no part of the claimed design.