Bump virtualenv from 20.2.1 to 20.4.3

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.2.1 to 20.4.3.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/main/docs/changelog.rst)
- [Commits](pypa/virtualenv@20.2.1...20.4.3)

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

Author: dependabot[bot]

setup.py

@@ -45,7 +45,7 @@
             "python-coveralls==2.9.3",
             "coverage==4.5.4",
             "mock==2.0.0",
-            "virtualenv==20.2.1",
+            "virtualenv==20.4.3",
         ],
     },
     classifiers=[