Bump virtualenv from 20.4.6 to 20.26.6

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.4.6 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@20.4.6...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

@@ -11,4 +11,4 @@ pytest-cov==2.11.1
 pytest-xdist==2.2.1
 pytest==6.2.4
 tox==3.23.1
-virtualenv==20.4.6
+virtualenv==20.26.6