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 dot-dash broken lines in the figures show features of an article of footwear that form no part of the claimed design. Further, the dot-dash broken lines immediately adjacent the portions shown in solid lines form the boundary of the design, with the broken lines forming no part of the claimed design. The even length broken lines in the figure views depict stitching, which forms no part of the claimed design.