The ornamental design for a lawn edging, as shown and described.
FIG. 1 is a front elevational view of the lawn edging showing my new design; the rear elevational view of the law edging corresponds to the front elevational view; and,
FIG. 2 is a top plan view of the lawn edging shown in FIG. 1; the bottom plan view of the lawn edging corresponds to the top plan view.