The ornamental design for the “bath brush,” as shown and described.
FIG. 1 is a perspective view of a bath brush;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof; and,
FIG. 6 is a top left side view thereof.
The broken lines are for illustrative purposes only and form no part of the claimed design. The cross-hatching in the drawing represents different types of mesh.