chore(deps): bump virtualenv in /.github/workflows (#29)

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.19.0 to 20.20.0.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/main/docs/changelog.rst)
- [Commits](pypa/virtualenv@20.19.0...20.20.0)

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

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

Author: dependabot[bot]

.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==20.19.0
+virtualenv==20.20.0