I claim the ornamental design for a sewn holster, as shown and described.
FIG. 1 is a perspective view of the sewn holster showing my new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a left side elevation view thereof; and,
FIG. 4 is a right side elevation view thereof.
The broken lines on the holster represent stitching, and are part of the claimed design. The dot-dashed broken lines of the second and fourth embodiment represent a boundary of the claimed design. The remaining broken lines of the second and fourth embodiment represent portions of the holster that form no part of the claimed design.