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