The ornamental design for a brace for a golfcart retractable awning, as shown and described.
FIG. 1 is a perspective view of a brace for a golf cart retractable awning showing my new design;
FIG. 2 is a left side elevation view thereof;
FIG. 3 is a right side elevation view thereof; and,
FIG. 4 is a top view.
The broken line showing the screw holes, the protruding screws and the connecting overlapping parts of the brace are included for the purpose of illustrating only and forms no part of the claimed design.