The ornamental design for a golf ball, as shown and described.
FIG. 1 is a top plan view of a golf ball showing our new design;
FIG. 2 is a bottom plan view thereof;
FIG. 3 is a front elevation thereof;
FIG. 4 is a rear elevation thereof;
FIG. 5 is a right side elevation thereof; and,
FIG. 6 is a left side elevation thereof.