Build(deps): Bump virtualenv from 20.5.0 to 20.6.0 in /.github/workfl…

…ows (#421)

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.5.0 to 20.6.0.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/main/docs/changelog.rst)
- [Commits](pypa/virtualenv@20.5.0...20.6.0)

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

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/constraints.txt

@@ -1,4 +1,4 @@
 pip==21.1.3
 nox==2021.6.12
 poetry==1.1.7
-virtualenv==20.5.0
+virtualenv==20.6.0