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. The even dashed broken lines in FIGS. 1-6 form no part of the claimed design. The dot-dot-dashed broken lines in FIGS. 1-6 represent boundary lines and form no part of the claimed design.