HACK: change mp_hal_stdout_tx_strn() to reporduce bug

This makes the function block forever without doing anything (other
than calling MICROPY_EVENT_POLL_HOOK in a loop.)

Author: dlech

bricks/_common_stm32/mphalport.c

@@ -130,7 +130,8 @@ int mp_hal_stdin_rx_chr(void) {
 void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
     while (len) {
         uint32_t size = len;
-        pbio_error_t err = pbsys_bluetooth_tx((const uint8_t *)str, &size);
+        // pbio_error_t err = pbsys_bluetooth_tx((const uint8_t *)str, &size);
+        pbio_error_t err = PBIO_ERROR_AGAIN;
 
         if (err == PBIO_SUCCESS) {
             str += size;