The ornamental design for a packagingbox, as shown and described.
FIG. 1 is a perspective view of the packaging box.
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; and,
FIG. 7 is a bottom view thereof.
The broken lines showing portions of a packaging box depicts only environment and forms no part of the claim. The dot-dash broken lines in the drawings represent an unclaimed boundary line and form no part of the claimed design.