We claim the ornamental design for a dust canister, as shown and described.
FIG. 1 is the front perspective view of a dust canister showing our new design;
FIG. 2 is the front view thereof;
FIG. 3 is the rear view thereof;
FIG. 4 is the left-side view thereof;
FIG. 5 is the right-side view thereof;
FIG. 6 is the top plan view thereof;
FIG. 7 is the bottom plan view thereof; and,
FIG. 8 is the rear-bottom perspective view thereof.
The broken lines in the drawings show parts of the dust canister that form no part of the claimed design. The shaded surfaces shown between the solid lines and the broken lines form part of the claim.