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

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.21.0 to 20.26.4.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/main/docs/changelog.rst)
- [Commits](pypa/virtualenv@20.21.0...20.26.4)

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

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

Author: dependabot[bot]

.github/workflows/constraints.txt

@@ -3,5 +3,5 @@ pip==23.1
 nox==2023.4.22
 nox-poetry==1.0.3
 poetry==1.4.2
-virtualenv==20.21.0
+virtualenv==20.26.4
 toml==0.10.2