The ornamental design for an earring, as shown and described.
FIG. 1 is a front perspective view of an earring;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a first side view thereof;
FIG. 5 is a second side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is a perspective view of the earring worn by a user.
The broken lines in the figures depict portions of the earring and environmental structure that form no part of the claimed design. The broken line showing of a person in FIG. 8 depicts environmental structure and is included for the purpose of showing the earring in a state of use.