ci: bump virtualenv from 20.30.0 to 20.31.1 in /.github/workflows

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.30.0 to 20.31.1.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/main/docs/changelog.rst)
- [Commits](pypa/virtualenv@20.30.0...20.31.1)

---
updated-dependencies:
- dependency-name: virtualenv
  dependency-version: 20.31.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

.github/workflows/constraints.txt

@@ -2,6 +2,6 @@ pip==25.1.1
 nox==2025.5.1
 nox-poetry==1.2.0
 poetry==1.8.5
-virtualenv==20.30.0
+virtualenv==20.31.1
 poetry-dynamic-versioning==1.8.2
 toml==0.10.2