build(deps): bump virtualenv in /.github/workflows

Bumps [virtualenv](/~https://github.com/pypa/virtualenv) from 20.20.0 to 20.21.0.
- [Release notes](/~https://github.com/pypa/virtualenv/releases)
- [Changelog](/~https://github.com/pypa/virtualenv/blob/20.21.0/docs/changelog.rst)
- [Commits](pypa/virtualenv@20.20.0...20.21.0)

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

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

.github/workflows/constraints.txt

@@ -2,4 +2,4 @@ pip==23.0.1
 nox==2022.11.21
 nox-poetry==1.0.2
 poetry==1.4.0
-virtualenv==20.20.0
+virtualenv==20.21.0