The ornamental design for a bathtubtoyfastener, as shown and described.
FIG. 1 is a top front isometric view of the bathtub toy fastener according to one embodiment of my new design;
FIG. 2 is a bottom isometric view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a left side view thereof;
FIG. 7 is a top view thereof; and,
FIG. 8 is a bottom view thereof.
In the drawings, the even dash-dash broken lines depicts portions of the bathtub toy fastener that forms no part of the claimed design. The long-short broken lines depict the boundary of the claim that form no part of the claimed design.