Update FYSETC S6 variant (#18331)

buildroot/share/PlatformIO/variants/FYSETC_S6/variant.h

 // Timer Definitions
 // Do not use timer used by PWM pin. See PinMap_PWM.
 #define TIMER_TONE              TIM6
-#define TIMER_SERVO             TIM2
+#define TIMER_SERVO             TIM5
 #define TIMER_SERIAL            TIM7
 
 // UART Definitions