I claim the ornamental design for an air freshener, as shown and described.
FIG. 1 is a front elevation view showing my new design; and,
FIG. 2 is a rear elevation view thereof.
More generally, the invention pertains to the design of an air freshener having front and back sides. The front and back sides compromise the design as illustrated. The air freshener may be used while suspended in the air, e.g., suspended from a rear-view mirror in a car.