The ornamental design for a switch, as shown and described.
FIG. 1 is a front view of a switch bearing the design;
FIG. 2 is a back view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a top view thereof;
FIG. 6 is a bottom view thereof; and,
FIG. 7 is a front-top-right perspective view thereof.
In the drawings, the claimed design is defined by the shaded surfaces; broken lines immediately adjacent shaded surfaces represent boundaries of the claim and form no part thereof; all other broken lines depict portions of the switch and form no part of the claim.