The ornamental design for a mitt, as shown and described.
FIG. 1 is a front plan view of the mitt,
FIG. 2 is an elevated perspective view of the mitt; and,
FIG. 3 is a bottom perspective view the mitt.
The surface treatment shown on the body of the mitt and the cross hatching shown on the band feature, both partially shown for ease of illustration, are understood to continue throughout the circumscribed areas. The broken line shown on the band represents stitching. The broken line shown on the bottom of the mitt in FIG. 3 represents the bounds of the claim and forms no part of the claimed design.