FIG. 1 is a perspective bottom/front view a lighting fixture showing my ornamental design; FIG. 2 is a perspective top/rear view thereof; FIG. 3 is an elevational right side view thereof, FIG. 4 is an elevational left side view thereof; FIG. 5 is a bottom plan view thereof; FIG. 6 is an elevational front view thereof; FIG. 7 is an elevational rear view thereof; and, FIG. 8 is a perspective bottom/front view thereof, showing an enlarged area.