We claim the ornamental design for a milking machine, as shown and described.
FIG. 1 is a rear elevation view of a milking machine in accordance with our new design;
FIG. 2 is a bottom plan view thereof;
FIG. 3 is an upper left front perspective view thereof; and,
FIG. 4 is an upper left rear perspective view thereof.
The broken line showing of a milker unit throughout the drawing figures depicts an exemplary component that forms no part of the claimed design but is included for illustrative purposes.