The ornamental design for a footrest, as shown and described.
FIG. 1 is a front, right-side, and top isometric view of a footrest showing the new design.
FIG. 2 is a front elevation view of the footrest.
FIG. 3 is a left-side elevation view.
FIG. 4 is a right-side elevation view.
FIG. 5 is a back elevation view.
FIG. 6 is a top plan view; and,
FIG. 7 is a bottom plan view.
The broken lines near the top front of the footrest (seen in FIGS. 1, 2, and 6) represent a trademark of the applicant and form no part of the claimed design. The broken lines on the back right side of the footrest (seen in FIGS. 1, 4, and 6) represent an inflation plug that also forms no part of the claimed design. The broken lines around an outer part of the top of the footrest (seen in FIGS. 1 and 6) represent stitching that also forms no part of the claimed design.