The ornamental design for a boot, as shown and described.
FIG. 1 is a perspective view of a boot, showing my new design; and,
FIG. 2 is an instep side perspective view thereof.
The broken lines around the football style lacing on the vamp represent claimed stitching.
The broken lines immediately adjacent the shaded areas represent the bounds of the claimed design while the broken lines showing the boot leg shaft, heel, sole, and NFL logo describe unclaimed subject matter.