Fix tethergun (#16612)

Content.Shared/Weapons/Misc/TetherGunComponent.cs

@@ -8,6 +8,12 @@ public sealed partial class TetherGunComponent : BaseForceGunComponent
     [ViewVariables(VVAccess.ReadWrite), DataField("maxDistance"), AutoNetworkedField]
     public float MaxDistance = 10f;
 
+    /// <summary>
+    /// The entity the tethered target has a joint to.
+    /// </summary>
+    [DataField("tetherEntity"), AutoNetworkedField]
+    public override EntityUid? TetherEntity { get; set; }
+
     /// <summary>
     /// The entity currently tethered.
     /// </summary>