The ornamental design for a multi-bulb spot lamp, as shown and described.
FIG. 1 is a top, front, and right side perspective view of a multi-bulb spot lamp, showing my new design; and,
FIG. 2 is a front elevational view thereof.
The broken lines shown in FIGS. 1 and 2 illustrate portions of the multi-bulb spot lamp that form no part of the claimed design. The boundary lines, shown in alternating long and short broken line segments, form no part of the claimed design.