The ornamental design for the ankle brace, as shown and described.
FIG. 1 is a right side perspective view of the ankle brace in fastened form where a wearer's foot and lower leg are in broken lines to show the environment of the invention, but form no part of it;
FIG. 2 is a right side perspective view of the ankle brace of FIG. 1 in isolation;
FIG. 3 is a left side perspective view of the ankle brace in fastened form;
FIG. 4 is a reduced right side perspective view of the ankle brace shown in FIG. 1 in unfastened form;
FIG. 5 is a reduced left side perspective view of the ankle brace shown in FIG. 2 in unfastened form;
FIG. 6 is a front perspective view of the ankle brace shown in FIG. 2; and,
FIG. 7 is a rear perspective view of the ankle brace shown in FIG. 2.
The dashed lines and zigzag lines on the ankle brace represent stitching and form no part of the claimed design. The shaded regions in FIGS. 1 through 7 represent no specific color or colors, but depict possible fabric or color variation and form no part of the claimed design.