tests/extmod/uctypes_array_assign_le: Fix buffer.

Structure descriptor in test extmod/uctypes_array_assign_le
is 6 bytes long, due to member "arr3" having length 4
(2 * UINT16) and offset 2, but only 5 bytes are allocated.
Increased buffer length to 6 bytes.

Signed-off-by: Duncan Lowther <Duncan.Lowther@glasgow.ac.uk>

tests/extmod/uctypes_array_assign_le.py

@@ -18,7 +18,7 @@
     "arr8": (uctypes.ARRAY | 1, 1, {"l": uctypes.UINT32 | 0}),
 }
 
-data = bytearray(5)
+data = bytearray(6)
 
 S = uctypes.struct(uctypes.addressof(data), desc, uctypes.LITTLE_ENDIAN)