The ornamental design for an actuatorbutton for a container, as shown and described.
FIG. 1 is a perspective view from front, above and one side of the actuator button for a container;
FIG. 2 is a front view of the actuator button for a container;
FIG. 3 is an enlarged perspective view from front, above and one side of the actuator button for a container; and,
FIG. 4 is an enlarged front view of the actuator button for a container.
In the drawings, the evenly-spaced broken lines showing portions of a container depict environment and form no part of the claim; the dash-dot-dot-dash line represents a boundary of the claimed design and forms no part thereof.