The ornamental design for a footwear upper, as shown and described.
FIG. 1. is a top front perspective view of a footwear upper embodying the new design;
FIG. 2. is a right side elevational view thereof; and,
FIG. 3. is a left side elevational view thereof.
FIG. 1-3 show features of an article of footwear in phantom lines formed by alternating long and short dashes: these features are shown for environmental purposes and do not form any part of the claimed design. FIG. 1-3 also show features of an article of footwear in broken lines formed by dashes of even length: these features represent stitching, which is part of the design.