deps(deps): update virtualenv requirement (#207)

Updates the requirements on [virtualenv](https://github.com/pypa/virtualenv) to permit the latest version.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/main/docs/changelog.rst)
- [Commits](pypa/virtualenv@21.5.1...21.6.0)

---
updated-dependencies:
- dependency-name: virtualenv
  dependency-version: 21.6.0
  dependency-type: direct:production
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

constraints.txt

@@ -12,7 +12,7 @@ aiohttp>=3.14.0,<4.0.0
 filelock>=3.29.6,<4.0.0
 # virtualenv: GHSA-597g-3phw-6986 (TOCTOU) - fix pending release (>20.36.1)
 # Using latest available until patch is released
-virtualenv>=21.5.1,<22.0.0
+virtualenv>=21.6.0,<22.0.0
 requests>=2.34.2,<3.0.0
 urllib3>=2.7.0,<3.0.0
 anyio>=4.14.1,<5.0.0