The ornamental injection device, as shown and described.
FIG. 1 is a top view of the injection device;
FIG. 2 is a bottom view of the injection device;
FIG. 3 is a right side view of the injection device;
FIG. 4 is a left side view of the injection device;
FIG. 5 is front end view of the injection device;
FIG. 6 is a rear end view of the injection device; and,
FIG. 7 is a perspective view of the injection device from the front and right.
The broken lines shown in the figures are for the purpose of illustrating portions of the article and forms no part of the claimed design. The broken line, which defines the bounds of the claimed invention, forms no part of the claimed design.