I claim the ornamental design for a shears, as shown and described.
FIG. 1 is a side elevation of a shears showing my new design.
FIG. 2 is a side elevation of the shears of FIG. 1 rotated 180 degrees; and,
FIG. 3 is a perspective view thereof in which a hand is shown in dashed lines to show the subject matter as it may be held. The hand is not part of the claimed design.