FIG. 1 is a bottom perspective view of a first embodiment of the luminaire mount showing the new design; FIG. 2 is a side elevational view thereof; FIG. 3 is a front elevational view thereof; FIG. 4 is a bottom view thereof; FIG. 5 is a top plan view thereof; FIG. 6 is a top perspective view thereof; FIG. 7 is a perspective view of a second embodiment of the luminaire mount of the new design shown inverted in an operational environment; FIG. 8 is a side elevational view thereof; FIG. 9 is a front elevational view thereof; FIG. 10 is a top plan view thereof; and, FIG. 11 is a bottom view thereof. The broken line environment showing is for illustrative purposes only and forms no part of the claimed design.