The ornamental design for a chisel, as shown and described.
FIG. 1 is a front perspective illustration of an embodiment of the chisel according to our design;
FIG. 2 is a rear perspective view thereof;
FIG. 3 is a front elevation view thereof;
FIG. 4 is a rear elevation view thereof
FIG. 5 is a left side view thereof, the right side being a mirror image thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
Where included, the broken line portions of the chisel form no part of the claimed design. Broken lines showing environment or structure are for illustrative purposes only and form no part of the claimed design.