The ornamental design for a wastebin, as shown and described.
FIG. 1 is a top plan view of a waste bin showing my new design;
FIG. 2 is a front elevational view thereof, with the left side elevational view, the right side elevational view, and the rear elevational view being identical thereto; and,
FIG. 3 is a top front perspective view thereof, with the top left side perspective view, the top right side perspective view, and the top rear perspective view being identical thereto.