The ornamental design for a shirt, as shown and described.
FIG. 1 is a front perspective view of a shirt showing our new design;
FIG. 2 is a front view thereof; and,
FIG. 3 is an enlarged view of FIG. 2 showing the shaded region enlarged for clarity.
The broken line immediately adjacent to the shaded area represents an unclaimed boundary of the claimed design. The broken line forms no part of the claimed design. The broken lines showing the remainder of the shirt and the unshaded regions therein are for environmental purposes only and form no part of the claimed design.