I claim the ornamental design for a decorative light, as shown and described.
FIG. 1 is a Perspective view of a decorative light showing my new design;
FIG. 2 is a Front view thereof;
FIG. 3 is a Back view thereof;
FIG. 4 is a Right-side view thereof;
FIG. 5 is a Left-side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines shown in drawings are included for the purpose of illustrating portions of the decorative light, and form no part of the claimed design.