We claim the ornamental design for a lighting fixture, as shown and described.
FIG. 1 is a front right perspective view thereof;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view.
The broken lines illustrate portions of the article which form no part of the claimed design. The area between the broken lines which indicate that the article is shown broken away forms no part of the claimed design. The cross-sectional shape of the article is understood to be uniform over the broken away portion and to match that of the adjacent portions.