all: Add missing imports for micropython.const.

Found by Ruff checking F821.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

examples/bluetooth/ble_uart_repl.py

@@ -7,6 +7,7 @@ import bluetooth
 import io
 import os
 import micropython
+from micropython import const
 import machine
 
 from ble_uart_peripheral import BLEUART