The ornamental design for a brush, as shown and described.
FIG. 1 is a right side elevational view showing a brush of my new design;
FIG. 2 is a rear elevational view thereof;
FIG. 3 is a left side elevational view thereof;
FIG. 4 is a front elevational view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof;
FIG. 7 is a perspective view thereof; and,
FIG. 8 is another perspective view thereof.
The broken lines showing of the brush handle, brush tips, and bristles in the drawings depict portions of the brush that form no part of the claimed design.