The ornamental design for a luminaire, as shown and described.
FIG. 1 is an upper perspective view of the luminaire of the present invention;
FIG. 2 is a front view of the design of the present invention;
FIG. 3 is a right side view of the design of the present invention. The left side is a mirror image of the right side, so the left side view is not depicted.
FIG. 4 is a top view of the design of the present invention; and,
FIG. 5 is a bottom view of the design of the present invention.
The broken lines showing environmental structure are for illustrative purposes only and form no part of the claimed design.