The ornamental design for an earring, as shown and described.
1. Earring
1.1: Perspective
1.2: Front
1.3: Back
1.4: Top
1.5: Bottom
1.6: Right
1.7: Left
1.8: In-use view for reference
The broken line showing of an ear in Fig. 1.8 depicts environment and forms no part of the claimed design. All other broken lines in the reproductions, including the faceted gemstones inset into the surface of the earring, depict portions of the earring that form no part of the claimed design.