build(deps): bump virtualenv from 20.25.0 to 20.26.6

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:production
...

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

Author: dependabot[bot]

requirements.txt

@@ -188,7 +188,7 @@ urllib3==1.26.18
     #   requests
     #   sentry-sdk
     #   teuthology (pyproject.toml)
-virtualenv==20.25.0
+virtualenv==20.26.6
     # via tox
 wcwidth==0.2.12
     # via prettytable