The ornamental design for a retractable toolbox, as shown and described.
FIG. 1 is a top view of a retractable tool box showing my new design;
FIG. 2 is a bottom view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a left side elevational view thereof; and,
FIG. 6 is a right side elevational view thereof.
The broken line “Makita” logo illustrates portions of the retractable tool box and forms no part of the claimed design. The “Makita” logo is a registered trademark of the MAKITA CORPERATION OF Japan.