The ornamental design for a garbagebagholder, as shown and described.
FIG. 1 is a front perspective view of the garbage bag holder;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a right elevation view thereof;
FIG. 5 is a left elevation view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a side view when the garbage bag holder is in a retracted position.
The broken lines depict portions of the garbage bag holder, which form no part of the claimed design. The garbage bag shown in broken lines is to show environment, and form no part of the claimed design.