The ornamental design for the assembly of gaming machines, as shown and described.
FIG. 1 is a perspective view of an assembly of gaming machines, the broken line showing is for illustrative purposes only, and forms no part of the claimed design.
FIG. 2 is a front elevational view of the assembly of the present invention;
FIG. 3 is a right side elevational view of the assembly of the present invention; and,
FIG. 4 is a left elevational view of the assembly of the present invention.