We claim the ornamental design for a ladder step barrier, as shown and described.
FIG. 1 is a perspective view of the ladder step barrier showing our new design;
FIG. 2 is another perspective view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a horizontal sectional view thereof, taken along line 4-4 of FIG. 3;
FIG. 5 is a bottom plan view thereof;
FIG. 6 is a rear elevational view thereof;
FIG. 7 is a front elevational view thereof;
FIG. 8 is a right side elevational view thereof; and,
FIG. 9 is a left side elevational view thereof.
The broken lines showing a ladder and four straps in FIG. 1 are for the purpose of illustrating environment and form no part of the claimed design. The broken lines showing four small openings on each corner of the ladder step barrier shown in FIGS. 1, 2, 3 and 5 are for the purpose of illustrating portions of the ladder step barrier and form no part of the claimed design.