The ornamental design for a containermountingbracket, as shown and described.
FIG. 1 is a front top perspective view of the container mounting bracket including broken lines, which are used in the present drawing and throughout the drawings to represent environment and which form no part of the claimed design;
FIG. 2 is a front top perspective view of the container mounting bracket, with a container disposed therein to show environment;
FIG. 3 is a top view of the container mounting bracket;
FIG. 4 is a front view of the container mounting bracket;
FIG. 5 is a back view of the container mounting bracket;
FIG. 6 is a right side view of the container mounting bracket, with left side being a mirror thereof, and,
FIG. 7 is a bottom view of the container mounting bracket.