The ornamental design for the walking cane, as shown and described.
FIG. 1 is a perspective view of the walking cane; and
FIG. 2 is a front plan view thereof; and
FIG. 3 is rear plan view thereof; and
FIG. 4 is a left side view thereof; and,
FIG. 5 is a right side view thereof.
The broken lines on the sole of the shoe in FIG. 2 form no part of the claimed design. The broken lines on the top portion of the shoe represent stitching.