The ornamental design for a toothbrush, as shown and described.
FIG. 1 is a perspective view of the toothbrush showing our new design;
FIG. 2 is a front view thereof:
FIG. 3 is a right side view thereof;
FIG. 4 is rear view thereof;
FIG. 5 is an enlarged partial right side view thereof;
FIG. 6 is an enlarged top view thereof; and,
FIG. 7 is an enlarged bottom view thereof.
The broken lines showing the bristles and the three small ribs on the front face of the head portion, the visible environmental structure of the handle, the elements on the rear of the head, and the elements on the distal end of the handle are for the purpose of illustrating portions of the toothbrush and form no part of the claimed design.