Plane: fixed motor test with DShot VTOL motors

need to arm when running the motor test

ArduPlane/AP_Arming.cpp

@@ -264,7 +264,7 @@ bool AP_Arming_Plane::disarm(const AP_Arming::Method method, bool do_disarm_chec
 
 void AP_Arming_Plane::update_soft_armed()
 {
-    hal.util->set_soft_armed(is_armed() &&
+    hal.util->set_soft_armed((plane.quadplane.motor_test.running || is_armed()) &&
                              hal.util->safety_switch_state() != AP_HAL::Util::SAFETY_DISARMED);
     AP::logger().set_vehicle_armed(hal.util->get_soft_armed());