The ornamental design for a footwear upper, as shown and described.
FIG. 1 is a top perspective view of a footwear upper showing my new design;
FIG. 2 is a first 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 broken line around the outsole perimeter forms a boundary of the claimed design and forms no part of the claimed design. The broken lines showing the footwear outsole and the footwear insole form no part of the claimed design.