The ornamental design for the headgear accessory, as shown and described.
FIG. 1 is a front perspective view of the headgear accessory, showing our new design, connected to an example headgear;
FIG. 2 is a bottom plan view of the headgear accessory connected to the example headgear;
FIG. 3 is a right side elevation view of the headgear accessory connected to the example headgear;
FIG. 4 is a left side elevation view of the headgear accessory connected to the example headgear; and
FIG. 5 is a top plan view of the headgear accessory; and,
FIG. 6 is a bottom plan view of the headgear accessory.
The headgear shown in broken lines in the drawings is environmental subject matter included to illustrate how the claimed design may appear when in use and forms no part of the claimed design. The longer-incremented broken lines shown in the headgear accessory itself is stitching and is a part of the claimed design.