[CHORE](deps-dev): Bump virtualenv from 20.25 to 20.26.6

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.25 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-version: 20.26.6
  dependency-type: direct:development
...

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

Author: dependabot[bot]

requirements-dev.txt

@@ -33,6 +33,6 @@ six==1.14.0
 toml==0.10.0
 tox==4.14.0
 traitlets==4.3.3
-virtualenv==20.25
+virtualenv==20.26.6
 wcwidth==0.1.9
 zipp==3.1.0