The ornamental design for a lightingfixture, as shown and described.
FIG. 1 is a front, bottom, and left side perspective view of a lighting fixture in a use environment;
FIG. 2 is another front, bottom, and left side perspective view thereof;
FIG. 3 is a left side elevational view thereof, the right side elevational view being a mirror image of the left side elevational view shown; and,
FIG. 4 is a bottom plan view thereof.
The broken lines in the drawings depict environmental subject matter only and form no part of the claimed design. The rear and top views, which are not shown in the drawings, form no part of the claimed design.