Bump virtualenv from 20.3.1 to 20.4.0
Bump virtualenv from 20.3.1 to 20.4.0

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.3.1 to 20.4.0.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/main/docs/changelog.rst)
- [Commits](https://github.com/pypa/virtualenv/compare/20.3.1...20.4.0)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
pydata/conf_site,pydata/conf_site,pydata/conf_site