The ornamental design for a lightingfixture, as shown and described.
1.1 is a perspective view showing of a lighting fixture showing our new design;
1.2 is a left side elevational view thereof;
1.3 is a right elevational view thereof;
1.4 is a front side elevational view thereof;
1.5 is a back side elevational view thereof;
1.6 is a bottom plan view thereof;
1.7 is a top plan view thereof.
The broken lines depicting the internal elements of the lighting fixture in the drawing are for illustrative purposes only and form no part of the claimed design.