The ornamental design for a trash can liner, as shown and described.
FIG. 1 is a top right perspective view of the trash can liner showing our new design;
FIG. 2 is a left side elevation view thereof, the right side elevation view being identical;
FIG. 3 is a front elevation view thereof, the rear elevation view being identical;
FIG. 4 is a top plan view thereof, the bottom plan view being identical; and,
FIG. 5 is a perspective view showing the liner in a deployed position.
The broken line showing of portions of the can and liner is included for purpose of illustrating environmental structure and forms no part of the claimed design.