The ornamental design for an accessory for a wheelbarrow, as shown and described.
FIG. 1 is a perspective view of the accessory for a wheelbarrow showing my new design.
FIG. 2 is a side elevation view thereof;
FIG. 3 is a front elevation view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a side elevation view wherein the accessory for a wheelbarrow is detached from the wheelbarrow; and,
FIG. 6 is a view of the accessory for a wheelbarrow in a folded configuration.
The dotted lines shown in the figures are representative of stitching on the accessory for a wheelbarrow. The features presented in broken lines show a wheelbarrow onto which the accessory for a wheelbarrow is attached and form no part of the claimed design.