tests/extmod/machine_uart_tx.py: Support STM32WB boards.

Signed-off-by: Damien George <[email protected]>

Author: dpgeorge

tests/extmod/machine_uart_tx.py

@@ -28,7 +28,10 @@
     initial_delay_ms = 20  # UART sends idle frame after init, so wait for that
     bit_margin = 1
 elif "pyboard" in sys.platform:
-    uart_id = 4
+    if "STM32WB" in sys.implementation._machine:
+        uart_id = "LP1"
+    else:
+        uart_id = 4
     pins = {}
     initial_delay_ms = 50  # UART sends idle frame after init, so wait for that
     bit_margin = 1  # first start-bit must wait to sync with the UART clock