We claim the ornamental design for a toothbrush, as shown and described.
FIG. 1 is a perspective view of the toothbrush;
FIG. 2 is a front elevation view of the toothbrush;
FIG. 3 is a back elevation view of the toothbrush;
FIG. 4 is a left side elevation view of the toothbrush;
FIG. 5 is a right side elevation view of the toothbrush;
FIG. 6 is a top plan view of the toothbrush;
FIG. 7 is a bottom plan view of the toothbrush; and,
FIG. 8 is an enlargement of area 8 shown in FIG. 1.
The broken lines shown in the drawings illustrate features of the article to which the design is applied or in which the design is embodied that form no part of the claim.