The ornamental design of a holder for a beverage container, as shown and described.
FIG. 1 is a front elevational view of a flat blank for a holder for a beverage container, showing one embodiment of the new design, the broken lines indicating an area where the holder is perforated;
FIG. 2 is a top plan view of the assembled holder for a beverage container of FIG. 1;
FIG. 3 is a front elevational view of the assembled holder for a beverage container of FIG. 1; and,
FIG. 4 is a side elevational view of the assembled holder for a beverage container of FIG. 1.