build(deps): bump virtualenv from 20.0.31 to 20.4.3

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.0.31 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@20.0.31...20.4.3)

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

Author: dependabot[bot]

requirements/test.txt

@@ -64,5 +64,5 @@ toml==0.10.1
 typed-ast==1.4.2
 typing-extensions==3.7.4.3
 # urllib3
-virtualenv==20.0.31
+virtualenv==20.4.3
 # zipp