venv in gitignore check unnecessary with virtualenv

[virtualenv](https://virtualenv.pypa.io/en/latest/) drops an "ignore all" `.gitignore` file into any virtualenvs it creates:

```
$ cat .venv/.gitignore
# created by virtualenv automatically
*
```

This feature will probably be upstreamed in Python too: https://github.com/python/cpython/issues/83417 . At that point, the fastdev check won't be required.