The ornamental design for an endbracket for a dual cassette roller shade, as shown and described.
FIG. 1 is an upper left side perspective view of the end bracket for a dual cassette roller shade;
FIG. 2 is a left side view of the end bracket for a dual cassette roller shade;
FIG. 3 is a right side view of the end bracket for a dual cassette roller shade; the broken lines in the drawing depict environmental subject matter only and form no part of the claimed design;
FIG. 4 is a front view of the end bracket for a dual cassette roller shade;
FIG. 5 is a rear view of the end bracket for a dual cassette roller shade;
FIG. 6 is a top view of the end bracket for a dual cassette roller shade; and,
FIG. 7 is a bottom view of the end bracket for a dual cassette roller shade.