Bump virtualenv from 20.26.6 to 20.28.0

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.26.6 to 20.28.0.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/main/docs/changelog.rst)
- [Commits](pypa/virtualenv@20.26.6...20.28.0)

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

Signed-off-by: dependabot[bot] <support@github.com>