I claim the ornamental design for a support step, as shown and described.
FIG. 1 is a perspective view of a support step, showing my new design;
FIG. 2 is an enlarged perspective view thereof;
FIG. 3 is a right-side elevational view of FIG. 2;
FIG. 4 is a left-side elevational view of FIG. 2;
FIG. 5 is a front elevational view of FIG. 2;
FIG. 6 is a rear elevational view of FIG. 2;
FIG. 7 is a top plan view of FIG. 2; and,
FIG. 8 is a bottom plan view of FIG. 2.
The broken lines showing a person using two of the designs on two wooden studs in FIG. 1, the text shown on the FIGS. 1, 7 and 8, and the areas bordered by broken lines in FIGS. 3, 5 and 8 depict environmental matter and form no part of the claimed design.