The ornamental design for a footwear upper, as shown and described.
FIG. 1 is a perspective view of a footwear upper showing my new design;
FIG. 2 is a side elevational view thereof;
FIG. 3 is an opposite side elevational view thereof;
FIG. 4 is a front elevational view thereof;
FIG. 5 is a rear elevational view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The dashed lines represents portions of the footwear that do not form any part of the claimed design. Further, the dash dot dot dash lines immediately adjacent to the solid-line portions of the footwear defines the bounds of the design, and forms no part of the claimed design.