The ornamental design for a goalpostgame, as shown and described.
FIG. 1 is a front view of the goal post game showing my new design;
FIG. 2 is a back view thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a bottom view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a left side view thereof; and,
FIG. 7 is a front perspective view thereof.
The broken lines showing an unclaimed target in the shape of a can in FIGS. 1-7 illustrates environmental subject matter and form no part of the claimed design.