Laser/spindle PWM off on M5

Marlin/src/gcode/control/M3-M5.cpp

 void GcodeSuite::M5() {
   stepper.synchronize();
   WRITE(SPINDLE_LASER_ENABLE_PIN, !SPINDLE_LASER_ENABLE_INVERT);
+  #if ENABLED(SPINDLE_LASER_PWM)
+    analogWrite(SPINDLE_LASER_PWM_PIN, SPINDLE_LASER_PWM_INVERT ? 255 : 0);
+  #endif
   delay_for_power_down();
 }