I claim the ornamental design for a lighting fixture, as shown and described.
The single FIGURE is a perspective front view of the light fixture showing the new design, for which the back perspective view would be identical. The shades have a circular horizontal cross section.
The broken lines immediately adjacent the shaded areas and the broken lines dividing the tips of the arcs from the rest of the arcs represent the bounds of the claimed design, while all other broken lines are directed to environment and are for illustrative purposes only. The broken lines form no part of the claimed design.