The ornamental design for a heel for footwear, as shown and described.
FIG. 1 is a front elevational view of a heel for footwear showing my new design;
FIG. 2 is a front left side isometric view thereof;
FIG. 3 is a left side elevational view thereof, the right side elevational view being a mirror image view thereof;
FIG. 4 is a right side isometric view thereof;
FIG. 5 is a bottom rear isometric view thereof;
FIG. 6 is a rear isometric view thereof; and,
FIG. 7 is a bottom isometric view thereof.
All surfaces not shown form no part of the claimed design. The broken lines shown in FIGS. 4-7 illustrate portions of the heel for footwear that form no part of the claimed design.