The ornamental design for a luminaire, as shown and described.
FIG. 1 is a top-down perspective view showing of a luminaire showing our new design;
FIG. 2 is a bottom-up perspective view showing of a luminaire showing our new design;
FIG. 3 is a front side elevational view thereof;
FIG. 4 is a back elevational view thereof;
FIG. 5 is a left side elevational view thereof;
FIG. 6 is a right side elevational view thereof;
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The dash-dot-dash broken lines shown represent the bounds of the claim and forms no part thereof and the dashed broken lines shown therein illustrate portions of the luminaire that form no part of the claimed design.