Bump virtualenv from 20.1.0 to 20.2.0 in /.github/workflows

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.1.0 to 20.2.0.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/main/docs/changelog.rst)
- [Commits](pypa/virtualenv@20.1.0...20.2.0)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/constraints.txt

@@ -1,4 +1,4 @@
 pip==20.2.4
 nox==2020.8.22
 poetry==1.1.4
-virtualenv==20.1.0
+virtualenv==20.2.0