The ornamental design for the ladder bracket, as shown and described.
FIG. 1 is a front perspective view of a ladder bracket showing my new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left side elevation view thereof;
FIG. 5 is a right side elevation view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines shown in the figures are included for the purposes of illustrating portions of the ladder bracket which form no part of the claimed design.