Bump virtualenv from 20.15.0 to 20.26.5 in /.github/workflows

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.15.0 to 20.26.5.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/main/docs/changelog.rst)
- [Commits](pypa/virtualenv@20.15.0...20.26.5)

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

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/constraints.txt

@@ -2,4 +2,4 @@ pip==23.0.1
 nox==2022.11.21
 nox-poetry==1.0.3
 poetry==1.4.2
-virtualenv==20.15.0
+virtualenv==20.26.5