We claim the ornamental design for a packaging box, as shown.
FIG. 1 is a front/right-side/top perspective view of a first embodiment of a packaging box showing our new design;
FIG. 2 is a front-side elevational view thereof;
FIG. 3 is a rear-side elevational view thereof;
FIG. 4 is a left-side elevational view thereof;
FIG. 5 is a right-side elevational view thereof;
FIG. 6 is a top-side elevational view thereof;
FIG. 7 is a bottom-side elevational view thereof; and,
FIG. 8 is a front/right-side/top perspective view of a second embodiment of our design similar to the first embodiment but having different proportions.