The ornamental design for a vest, as shown and described.
FIG. 1 is a perspective view of a vest showing my new design;
FIG. 2 is a right side view of the vest;
FIG. 3 is a top view of the vest;
FIG. 4 is a front view of the vest;
FIG. 5 is a rear side view of the vest;
FIG. 6 is a left view of the vest;
FIG. 7 is a bottom view of the vest; and,
FIG. 8 is a perspective view of the vest with a nut.
The broken lines in FIGS. 1 and 8 depicting a person represent environmental subject matter that forms no part of the claimed design. The broken lines of FIG. 8 depicting a nut represents portions of the vest that form no part of the claimed design.