Bump virtualenv from 20.25.0 to 20.26.6 in /docker

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] <[email protected]>

Author: dependabot[bot]

docker/requirements.txt

@@ -17,7 +17,7 @@ platformdirs==4.2.0
 pyelftools==0.28
 pyparsing==3.0.9
 typing-extensions==4.3.0
-virtualenv==20.25.0
+virtualenv==20.26.6
 wheel==0.38.4
 
 # The following packages are considered to be unsafe in a requirements file: