The ornamental design for an headlight for a vehicle, as shown and described.
FIG. 1 is a perspective view of an headlight for a vehicle according to the novel design;
FIG. 2 is left side view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is another perspective view thereof; and,
FIG. 6 is the top plan view.
The broken lines are for environmental purposes only and form no part of the claimed design. The design shown is not to be limited to any particular size and may be scaled larger or smaller. The drawings and descriptions represent the right side embodiment. The claim is also for a mirror image of a left side embodiment that is not shown.