venv in gitignore check unnecessary with virtualenv

[adamchainz]

virtualenv 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.