The ornamental design for a groundstakepuller, as shown and described.
FIG. 1 is a top plan view of the ground stake puller showing my new design;
FIG. 2 is a bottom plan view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a right side view thereof; and,
FIG. 7 is a perspective view thereof.
The broken lines depict portions of the ground stake puller in which the design is embodied that form no part of the claimed design. The surface shading illustrated in the drawings is provided merely to describe the form of the design; it is not intended to be illustrative of texture or gloss.