The ornamental design for a storage tray, as shown and described.
FIG. 1 is a forward left-side perspective view of the storage tray showing my new design;
FIG. 2 is a rearward right-side perspective view thereof; and,
FIG. 3 is a top view thereof.
The broken line showings of the lever handle, the rear storage area, the border around the front storage area, and the ledge located within the forward portion of the front storage area are for illustrative purposes only and form no part of the claimed design.