Bump virtualenv from 20.38.0 to 21.1.0 (#169)

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.38.0 to 21.1.0.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/main/docs/changelog.rst)
- [Commits](pypa/virtualenv@20.38.0...21.1.0)

---
updated-dependencies:
- dependency-name: virtualenv
  dependency-version: 21.1.0
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

requirements-dev.txt

@@ -63,7 +63,7 @@ ruff==0.15.4
     # via ccs-govuk-frontend-jinja (pyproject.toml)
 typing-extensions==4.15.0
     # via mypy
-virtualenv==20.38.0
+virtualenv==21.1.0
     # via pre-commit
 werkzeug==3.1.6
     # via flask