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 illustrate portions of the footwear that forms no part of the claimed design. The dash dot dash lines immediately adjacent to the solid-line portions of the footwear define the bounds of the claimed design and form no part thereof.