The ornamental design for a shirt, as shown and described.
FIG. 1 is a front left perspective view of a shirt showing my new design in an in-use configuration;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines immediately adjacent to the shaded area represent unclaimed boundaries of the design. The unshaded regions, demarcated by broken lines, represent unclaimed portions of the shirt and form no part of the claimed design.