I claim, the ornamental design for a seat, as shown and described.
FIG. 1 is a perspective view of a seat, showing our new design, and including portions shown in broken lines herein and throughout for purposes of illustration only and forming no part of the claimed design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a side elevation view thereof taken from the right of FIG. 1, the opposite side being a mirror image; and