The ornamental design for a petbed, as shown and described.
FIG. 1 is a perspective view of a pet bed, showing my new design.
FIG. 2 is a top plan view thereof;
FIG. 3 is a right side elevation view thereof; the left side elevational is a mirror image;
FIG. 4 is a front view thereof;
FIG. 5 is a rear view thereof; and,
FIG. 6 is a bottom plan view thereof.
The dash-dash broken lines illustrate stitching that forms no part of the claimed design. The dot-dot broken lines illustrate the contours of the portions of the pet bed that form part of the claimed design.