tests/pyb: Adjust UART and Timer tests to work on PYBD_SF6.

tests/pyb/timer.py

@@ -16,4 +16,4 @@ print(tim.period())
 tim = Timer(2, freq=100)
 print(tim.freq())
 tim.freq(0.001)
-print(tim.freq())
+print('{:.3f}'.format(tim.freq()))

tests/pyb/uart.py

 from pyb import UART
 
 # test we can correctly create by id
-for bus in (-1, 0, 1, 2, 5, 6, 7):
+for bus in (-1, 0, 1, 2, 5, 6):
     try:
         UART(bus, 9600)
         print("UART", bus)

tests/pyb/uart.py.exp

@@ -4,7 +4,6 @@ UART 1
 UART 2
 ValueError 5
 UART 6
-ValueError 7
 UART(1, baudrate=9600, bits=8, parity=None, stop=1, flow=0, timeout=0, timeout_char=3, rxbuf=64)
 UART(1, baudrate=2400, bits=8, parity=None, stop=1, flow=0, timeout=0, timeout_char=7, rxbuf=64)
 0