The ornamental design for boot, as shown and described.
FIG. 1 is a rear perspective view of a boot showing my new design;
FIG. 2 is a rear view thereof;
FIG. 3 is a first side view thereof;
FIG. 4 is a second side view thereof; and,
FIG. 5 is a bottom view thereof.
The dash-dash broken lines shown in the drawings represent unclaimed environment and are for illustrative purposes only, forming no part of the claimed design.