RuntimeWarning: line buffering (buffering=1) isn't supported in binary mode with Python 3.8

Running latest codespell under Python 3.8 results in the following warning:
```
.pyenv/versions/3.8.0/lib/python3.8/codecs.py:905: RuntimeWarning: line buffering (buffering=1) isn't supported in binary mode, the default buffer size will be used
  file = builtins.open(filename, mode, buffering)
```

This was introduced in Python 3.8 here:
https://bugs.python.org/issue32236