The ornamental design for a shirt, as shown and described herein.
FIG. 1 is a front, isometric view of a shirt in accordance with the present invention;
FIG. 2 is a front view of the shirt of FIG. 1;
FIG. 3 is a rear view of the shirt of FIG. 1;
FIG. 4 is a side view of the shirt of FIG. 1; and,
FIG. 5 is another side view of the shirt of FIG. 1.
Those portions of the shirt shown in broken lines are included for illustrative purposes only, including the zippers on the cuffs, and form no part of the presently claimed design.