The ornamental design for a containersleeve, as shown and described.
FIG. 1 is a first perspective view;
FIG. 2 is a second perspective view;
FIG. 3 is a first side view;
FIG. 4 is a second side view;
FIG. 5 is a third side view;
FIG. 6 is a fourth side view;
FIG. 7 is a top view; and,
FIG. 8 is a bottom view.
The dashed lines depict portions of the container sleeve that form no part of the claimed design. The dash dot dot lines depict stitching of the container sleeve that forms no part of the claimed design.