ntpath.normpath('\\\\') produces different result on Windows 

In Python 3.11.0rc1 on Windows:

```python
>>> import ntpath
>>> ntpath.normpath('\\\\')
'\\\\'
```

In Python 3.11.0rc1 on non-Windows platforms, and in 3.10 across all platforms:

```python
>>> import ntpath
>>> ntpath.normpath('\\\\')
'\\'
```


### Linked PRs
* gh-100351
* gh-100999