Bump virtualenv from 16.2.0 to 20.0.29

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 16.2.0 to 20.0.29.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/master/docs/changelog.rst)
- [Commits](https://github.com/pypa/virtualenv/compare/16.2.0...20.0.29)

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

requirements-indirect.txt

@@ -24,5 +24,5 @@ smmap==3.0.4
 smmap2==3.0.1
 toml==0.10.1
 tox==2.9.1
-virtualenv==16.2.0
+virtualenv==20.0.29
 wcwidth==0.1.9