The ornamental design for a toothbrush accessory, as shown and described.
FIG. 1 is a front perspective view of a toothbrush accessory showing my new design;
FIG. 2 is a front perspective with toothbrush and toothpaste;
FIG. 3 is a front plan view thereof;
FIG. 4 is a rear plan view thereof
FIG. 5 is a left-side plan view thereof;
FIG. 6 is a right-side plan view thereof.
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The raised surface treatment applied to the outer surface is understood to extend uniformly across all the surfaces to which they are applied.
The broken line showing of the toothbrush and toothpaste is included for the purpose of illustrating environment and forms no part of the claimed design.