The ornamental design for a developingcartridge, as shown and described.
FIG. 1 is a front perspective view of front, top and right side of a developing cartridge showing my new design;
FIG. 2 is a rear perspective view of rear, bottom and left side thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The broken lines in the figures are included for the purpose of illustrating portions of the developing cartridge that form no part of the claimed design.