Bump virtualenv from 20.25.0 to 20.26.6 in /requirements

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.25.0 to 20.26.6.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/main/docs/changelog.rst)
- [Commits](pypa/virtualenv@20.25.0...20.26.6)

---
updated-dependencies:
- dependency-name: virtualenv
  dependency-type: direct:development
...

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

Author: dependabot[bot]

requirements/dev_3.11.txt

@@ -716,7 +716,7 @@ urllib3==2.0.7
     #   requests
 validate-pyproject==0.15
     # via efaar-benchmarking (pyproject.toml)
-virtualenv==20.25.0
+virtualenv==20.26.6
     # via
     #   pre-commit
     #   tox