The ornamental design for a shirt, as shown and described.
FIG. 1 is a front view of a shirt according to the design;
FIG. 2 is a rear view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a front perspective view thereof;
FIG. 6 is a rear perspective view thereof;
FIG. 7 is a front view thereof shown in an environment of use; and,
FIG. 8 is a rear view thereof shown in an environment of use.
The broken line showing of the hands, arms, legs, torso, neck, and head in FIGS. 7-8 is for the purpose of illustrating portions of the environmental structure and forms no part of the claimed design.