The ornamental design for a harness for pets, as shown and described.
1. Harness for pets
1.1 : Perspective
1.2 : Front
1.3 : Back
1.4 : Left
1.5 : Right
1.6 : Top
1.7 : Bottom
1. This article according to the present design is made of synthetic fiber, synthetic resin, and metal; 2. This article according to the present design is worn on a pet, and includes rings to which a strap is connected; 3. Figure 1.1 is a perspective view of the present design, Figure 1.2 is a front view of the present design, Figure 1.3 is a rear view of the present design, Figure 1.4 is a left side view of the present design, Figure 1.5 is a right side view of the present design, Figure 1.6 is a top view of the present design, and Figure 1.7 is a bottom view of the present design.