The ornamental design for a side brush, as shown and described.
FIG. 1 is a front elevation view of a side brush in accordance with the present invention;
FIG. 2 is a rear elevation view of the side brush thereof;
FIG. 3 is a left side elevation view thereof;
FIG. 4 is a rear elevation view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof;
FIG. 7 is a bottom and left side perspective view thereof; and,
FIG. 8 is a front, top and right side perspective view thereof.
The features shown in broken lines in the drawings illustrate portions of the article in which the design is embodied or applied that form no part of the claim.