The ornamental design for a laundry bin, as shown and described.
FIG. 1 is a front perspective view of a laundry bin;
FIG. 2 is a top plan view thereof; and,
FIG. 3 is a side perspective view thereof.
The other side view thereof is a mirror image of the side view shown in FIG. 3.
The bag shown in broken lines inserted in the laundry bin in FIGS. 1 and 3 is environmental structure shown for illustrative purposes only and does not form any part of the claimed design.