The ornamental design for a footwear upper, as shown and described.
FIG. 1 is a perspective view of the footwear upper embodying the new design;
FIG. 2 is a top view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a front view thereof; and,
FIG. 6 is a rear view thereof.
The figures show features of an article of footwear in broken lines that do not form any part of the claimed design. Further, the broken lines immediately adjacent the solid line portions of the design form the boundary of the design, with the broken lines forming no part of the claimed design.