I claim the ornamental design for a toolbox, as shown and described.
FIG. 1 is a front view of a toolbox showing my new design;
FIG. 2 is a rear perspective view thereof;
FIG. 3 is a left-side view thereof;
FIG. 4 is a right-side view thereof;
FIG. 5 is a top view thereof;
FIG. 6 is a bottom view thereof;
FIG. 7 is a front perspective view thereof; and,
FIG. 8 is a rear perspective view thereof.
The shade lines shown in the drawings represent the contour of the surfaces and not surface ornamentation. The broken lines illustrate portions of the toolbox and form no part of the claimed design.