The ornamental design for a sleeve, as shown and described.
FIG. 1 is a front view of a sleeve;
FIG. 2 is a rear view thereof;
FIG. 3 is a left view thereof;
FIG. 4 is a right view thereof;
FIG. 5 is a top view thereof;
FIG. 6 is a bottom plan view thereof; and,
FIG. 7 is a perspective view thereof.
The broken line showing arm, person, and clothing is included for the purpose of illustrating environmental structure and forms no part of the claimed design.