Bump virtualenv from 20.25.1 to 20.26.6 in /requirements

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.25.1 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@20.25.1...20.26.6)

---
updated-dependencies:
- dependency-name: virtualenv
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements/dev.txt

@@ -22,7 +22,7 @@ pyyaml==6.0.1
     # via pre-commit
 ruff==0.3.4
     # via -r dev.in
-virtualenv==20.25.1
+virtualenv==20.26.6
     # via pre-commit
 
 # The following packages are considered to be unsafe in a requirements file: