We claim the ornamental design for a brush assembly, as shown and described.
FIG. 1 is a perspective view of a brush assembly showing the new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof,
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The present application is directed to the design illustrated in the drawings. The broken lines represent environmental structure of the brush assembly and form no part of the claimed design.