Bump virtualenv from 20.8.0 to 20.8.1 in /.github/workflows

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.8.0 to 20.8.1.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/main/docs/changelog.rst)
- [Commits](pypa/virtualenv@20.8.0...20.8.1)

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

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

Author: dependabot[bot]

.github/workflows/constraints.txt

@@ -4,4 +4,4 @@ nox==2021.10.1
 nox-poetry==0.8.6
 poetry==1.1.11
 pre-commit==2.15.0
-virtualenv==20.8.0
+virtualenv==20.8.1