The ornamental design for a taco shell holder, as shown and described.
FIG. 1 is a front perspective view of the subject taco shell holder for holding a taco shell in an upright manner;
FIG. 2 is a rear perspective view of the taco shell holder for holding the taco shell; and,
FIG. 3 is a perspective view of the taco shell holder illustrating a portion of the holder releasably attached to the side of a dinner plate.
The broken lines in FIG. 3 illustrating the dinner plate, food items on the dinner plate and the taco shell with food items therein are for illustrative purposes only and form no part of the invention.