Bump virtualenv from 20.16.3 to 20.16.4 (#4)

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.16.3 to 20.16.4.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/main/docs/changelog.rst)
- [Commits](pypa/virtualenv@20.16.3...20.16.4)

---
updated-dependencies:
- dependency-name: virtualenv
  dependency-type: indirect
  update-type: version-update:semver-patch
...

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