Type error happened when join byte string.

[aT0ngMu]

Hi, when I tested _buffer_encode() in class IncrementalEncoder, I found that function alabel() would return bytes-string, which causes the elements of the result list to be of type bytes. However, the join method can only receive parameters of type str, which will cause the program to crash.

The following is the crash stack information:

=== Uncaught Python exception: ===
TypeError: sequence item 0: expected str instance, bytes found
Traceback (most recent call last):
File "incrementalEncoder_driver.py", line 25, in TestOneInput
instance._buffer_encode(data=argStr0,errors="strict",final=argBool2)
File "/home/server1/yuxinwei/DriverCollections/venv/lib/python3.8/site-packages/idna/codec.py", line 57, in _buffer_encode
result_str = '.'.join(result) + trailing_dot # type: ignore
TypeError: sequence item 0: expected str instance, bytes found