The ornamental design for a vest, as shown and described.
FIG. 1 is a front perspective view of a vest showing my design;
FIG. 2 is a front view thereof;
FIG. 3 is a first side view thereof;
FIG. 4 is a second side view thereof; and,
FIG. 5 is a rear view thereof.
The dash lines in FIGS. 1-4 indicate stitching and form part of the claimed design. The long dash with two short dash broken lines illustrate portions of the article and form no part of the claim. The long dash with two dot broken lines define the bounds of the claimed design and form no part thereof.