The ornamental design for a step, as shown and described.
FIG. 1 is a left-front perspective view of the step from above.
FIG. 2 is a top view of the step.
FIG. 3 is a front view of the step. Other than brackets affixed to feet of the step, which are illustrated in broken lines, the step has front-to-rear mirror-image symmetry; and,
FIG. 4 is a left side view of the step. Other than brackets affixed to feet of the step, which are illustrated in broken lines, the step has left-to-right mirror-image symmetry.
The broken lines in the figures depict portions of the step that form no part of the claimed design.