`sys.stdout` has no attribute `buffer`

If I run
```
import sys
sys.stdout.buffer
```
in a Python or a IPython shell, it works fine:

```python
In [1]: import sys

In [2]: sys.stdout.buffer
Out[2]: <_io.BufferedWriter name=''>
```

However, when running in a Jupyter Notebook, I get:
```python-traceback
AttributeError Traceback (most recent call last)
/var/folders/hp/166tdb592211tp23nb_rgmqw0000gp/T/ipykernel_3131/3028238189.py in
----> 1 sys.stdout.buffer

AttributeError: 'OutStream' object has no attribute 'buffer'
```

Some diagnostics:
```console
$ pip freeze | grep ipykernel
ipykernel==6.4.1
$ python --version
Python 3.9.6
```

---

Noticed when looking into https://github.com/psf/black/issues/2516