We claim the ornamental design for a cage joining lock, as shown and described.
FIG. 1 is a top plan view of a cage joining lock showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a left side elevational view thereof;
FIG. 4 is a right side elevational view thereof;
FIG. 5 is a rear elevational view thereof;
FIG. 6 is a bottom plan view thereof; and,
FIG. 7 is a perspective view thereof.
The dashed lines are for the purpose of illustrating optional portions of the cage joining lock and form no part of the claimed design. The broken lines on the surface portions indicate contour and not surface decoration.