I claim the ornamental design for a pet litter scoop, as shown and described.
FIG. 1 is a perspective view of the pet litter scoop.
FIG. 2 is a top view of the pet litter scoop.
FIG. 3 is a bottom view of the pet litter scoop.
FIG. 4 is a left side view of the pet litter scoop.
FIG. 5 is a right side view of the pet litter scoop.
FIG. 6 is a front view of the pet litter scoop; and,
FIG. 7 is a rear view of the pet litter scoop.
The illustrative broken line showing of a handle body throughout the drawing figures depicts an exemplary component of the pet litter scoop that does not form part of the claimed design.