Set the correct task action for the long-range gravity task.

src/task.c

@@ -176,13 +176,13 @@ __attribute__((always_inline)) INLINE static enum task_actions task_acts_on(
 
     case task_type_init_grav:
     case task_type_grav_mm:
+    case task_type_grav_long_range:
       return task_action_multipole;
       break;
 
     case task_type_drift_gpart:
     case task_type_grav_down:
     case task_type_grav_mesh:
-    case task_type_grav_long_range:
       return task_action_gpart;
       break;