We claim the ornamental design for an kettle grill accessory, as shown and described.
FIG. 1 is an environmental perspective view of the kettle grill accessory;
FIG. 2 is a top perspective view of the kettle grill accessory;
FIG. 3 is a bottom perspective view of the kettle grill accessory;
FIG. 4 is a first side view of the kettle grill accessory;
FIG. 5 is a top view of the kettle grill accessory;
FIG. 6 is a second side view of the kettle grill accessory;
FIG. 7 is a bottom view of the kettle grill accessory;
FIG. 8 is a first end view of the kettle grill accessory; and,
FIG. 9 is a second end view of the kettle grill accessory.
The structure of the kettle grill accessory shown in broken lines in the drawings forms no part of the claimed design. In FIG. 1, the broken lines representing a kettle grill are for environmental purposes, and likewise form no part of the claimed design.