Bump virtualenv from 20.6.0 to 20.26.6

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.6.0 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@20.6.0...20.26.6)

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

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

requirements-dev.txt

@@ -17,4 +17,4 @@ pyparsing==2.4.7
 pytest==6.2.5
 requirements-tools==2.0.0
 toml==0.10.2
-virtualenv==20.6.0
+virtualenv==20.26.6