tests: Update pyb/uart.py test since baudrate of 1200 is too low.

tests/pyb/uart.py

@@ -5,7 +5,7 @@ uart = UART(1, 9600)
 uart = UART(1, 9600, bits=8, parity=None, stop=1)
 print(uart)
 
-uart.init(1200)
+uart.init(2400)
 print(uart)
 
 print(uart.any())

tests/pyb/uart.py.exp

 UART(1, baudrate=9600, bits=8, parity=None, stop=1, timeout=1000, timeout_char=0, read_buf_len=64)
-UART(1, baudrate=1200, bits=8, parity=None, stop=1, timeout=1000, timeout_char=0, read_buf_len=64)
+UART(1, baudrate=2400, bits=8, parity=None, stop=1, timeout=1000, timeout_char=0, read_buf_len=64)
 False
 3
 4