The ornamental design for a tub spout, as shown and described.
FIG. 1 is a perspective view of a tub spout showing my new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a bottom view thereof;
FIG. 4 is a left side view thereof, the opposite side being a mirror image of the side shown;
FIG. 5 is a front end view thereof; and,
FIG. 6 is a rear end view thereof.
The broken lines showing portions of the tub spout are included for the purpose of illustrating the environmental structure and form no part of the claimed design.