Fix BUILTIN_LED to target red LED at the back

Author: francisduvivier

variants/fri3d_2024_esp32s3/pins_arduino.h

@@ -11,10 +11,7 @@
 #define NUM_DIGITAL_PINS        48
 #define NUM_ANALOG_INPUTS       20
 
-// Some boards have too low voltage on this pin (board design bug)
-// Use different pin with 3V and connect with 48
-// and change this setup for the chosen pin (for example 38)
-static const uint8_t LED_BUILTIN = SOC_GPIO_PIN_COUNT+7;
+static const uint8_t LED_BUILTIN = 21;
 #define BUILTIN_LED  LED_BUILTIN // backward compatibility
 #define LED_BUILTIN LED_BUILTIN
 #define RGB_BUILTIN LED_BUILTIN