I claim the ornamental design for the collapsible salad spinner strainer basket, as shown and described.
FIG. 1 is a perspective view of the collapsible salad spinner strainer basket, showing my new design;
FIG. 2 is a front view of the collapsible salad spinner strainer basket, the back, left side, and right side views being identical;
FIG. 3 is a top view of the collapsible salad spinner strainer basket;
FIG. 4 is a bottom view of the collapsible salad spinner strainer basket; and,
FIG. 5 is an exploded view of the collapsible salad spinner strainer basket, shown together with a representative lid and bowl in which the lid and bowl are shown in phantom and form no part of the claimed invention.