The ornamental design for a leash, as shown and described.
FIG. 1 is a perspective view of a leash shown in a state of use in accordance with the present invention;
FIG. 2 is a front view of the leash shown in an alternate configuration;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken line showing of a post in FIG. 1 illustrates environmental structure that forms no part of the claimed design. The broken lines shown in FIGS. 1-3 depict stitching and form part of the claimed design.