Bump virtualenv from 21.2.4 to 21.3.0

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 21.2.4 to 21.3.0.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/main/docs/changelog.rst)
- [Commits](pypa/virtualenv@21.2.4...21.3.0)

---
updated-dependencies:
- dependency-name: virtualenv
  dependency-version: 21.3.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

example/requirements.txt

@@ -1,3 +1,3 @@
 glob2==0.4.1
 hellbox==0.1.3
-virtualenv==21.2.4
+virtualenv==21.3.0